Nuna LUMN vs. Britax Grow With You ClickTight | Harness to Booster Car Seat Comparison

Car seats can be confusing as there are so many different types - Infant, Convertible, Booster, and All-In-One, but there is one lesser known car seat called the Combination Seat or Harness to Booster Car Seat. The Harness to Booster style seat is a forward-facing only harness seat that later transitions to a booster seat using the vehicle seat belt. These seats are best for children ages 3 years old and up as they transition to forward facing. 

In this comparison, we’ll take a closer look at two highly respected car seat brands - Nuna and Britax - and their Combination Seats: the Nuna LUMN and the Britax Grow With You ClickTight Harness-2-Booster Car Seat. Both brands are known for producing high-quality, safe, easy to use car seats, but they bring different strengths to the table. Let's dive in! 

Nuna vs. Britax

Founded in 2007, Nuna has earned a reputation for designing high-quality, thoughtfully crafted products that prioritize both safety and convenience. Nuna is new to the Combination Seat category but has built a strong reputation with its sleek, modern designs and user-friendly features. They’re especially well-known for their lightweight infant seats, their rotating REVV car seat, their easy-to-install RAVA convertible seat, and their luxe all-in-one option, the EXEC. The Nuna LUMN, their first harness-to-booster seat, is an exciting new addition that brings the brand’s signature style and safety into the next stage of car seat use.

Britax has been in the car seat game for decades and is known for their strong emphasis on safety and innovation. Their Grow With You ClickTight Harness-2-Booster Car Seat is a standout in this category, offering multiple recline positions, easy installation with ClickTight technology, and exceptional side-impact protection. It’s a trusted choice for parents looking for a seat that truly grows with their child.

Benefits and Usefulness of a Harness to Booster Car Seat

Some parents may be wondering why do I need a harness to booster car seat? There are many circumstances that this type of car seat would be extremely beneficial. Let's take a look at a few real life examples:

Many parents have a 2 to 3 year age-gap between children. Once their youngest child reaches a year old, they're ready to transition them to a rear-facing convertible car seat. But they already have one for their 3 or 4 year old child. They decide they'd rather not buy another convertible car seat, and instead want to give that seat to their youngest child. Makes sense! But what seat will the 3 or 4 year old transition to? They are definitely not ready for a booster car seat - too wiggly, not mature enough, and possibly not even heavy enough. Unfortunately, we do see a lot of kids moving to a booster seat too early and part of that is parents just don't know that these type of Harness to Booster Seats exist. Enter the Nuna LUMN or Britax Grow With You ClickTight Harness to Booster Car Seat! This scenario is super common and these seats would be a perfect choice for these families. 

Another common scenario families face is when a child starts noticing their friends riding in “big kid” booster seats and begins pressuring their parents to ditch the “baby” seat. Or they've outgrown or are close to outgrowing their harnessed convertible seat, but they're not ready for a full on booster seat. A transitional combination seat offers the perfect solution. It gives kids that grown-up feel they’re craving, while still keeping them safely secured with a 5-point harness for longer. It’s a win-win, especially since booster seats require a lot of maturity from the child, who must stay properly seated for the entire ride. Harness-to-Booster seats like the Nuna LUMN and Britax Grow With You ClickTight strike that ideal balance, letting your child feel more independent while giving you the peace of mind that comes with extended harness use before switching to the vehicle seat belt. Both the Nuna and Britax seats feature higher top harness slots, allowing children to stay harnessed longer than in a typical convertible seat.

One last real life scenario we see often is when parents need another car seat for a caregiver or grandparent, but their child is already forward facing. Instead of purchasing a convertible car seat that they won't ever use the rear-facing mode, they can opt for a Harness to Booster car seat so their little one can stay harnessed, but have a seat that can continue to grow with them to the next stage car seat - the booster mode! 

Comparing Safety Features: Nuna LUMN vs. Britax Grow With You ClickTight

When it comes to safety, both the Nuna LUMN and the Britax Grow With You ClickTight  are top-tier options, each offering a robust set of features designed to protect your child. 

Britax stands out with its patented ClickTight® Installation system, which takes the guesswork out of a secure install—just open, thread and buckle the seat belt, and click it shut. The Grow With You seat also includes two layers of side impact protection that shield the head, neck, and torso, along with SafeCell Impact Technology built into the base to act as a crumple zone in a crash. An energy-absorbing V-shaped tether, industrial-strength steel frame, and energy-absorbing chest pads all work together to provide layered crash protection that parents can trust. Britax also now offers flame-retardant-free options, giving health-conscious parents even more reason to feel confident in their choice.

The Nuna LUMN matches that commitment to safety with a thoughtfully engineered design that includes an all-steel frame, reinforced belt path, and Aeroflex™ side impact protection system made of energy-absorbing EPP foam. Certified to meet the latest frontal and side-impact standards (FMVSS No. 213a and 213b), the LUMN also features a True Tension™ door, which—much like Britax’s ClickTight® system—creates a secure, no-fuss installation using the vehicle’s seat belt. Both systems function similarly by locking the belt tightly into place, eliminating common installation errors and ensuring peace of mind for parents. The LUMN also includes push-on LATCH connectors and an open belt path for easier booster-mode buckling. With added benefits like flame-retardant-free materials and GREENGUARD Gold Certification for low chemical emissions, the Nuna LUMN goes beyond crash protection to support long-term health and comfort as well.

Full List of Features: Nuna LUMN vs. Britax Grow With You ClickTight

Nuna LUMN Features

• 5-point no-rethread harness stows away when converting to booster
• 9 recline options in both harness and booster modes when tethered
• Bubble-free recline guides confirm the perfect riding angle
• 10-position height-adjustable headrest to accommodate growth
• Machine-washable fabrics and inserts– seat pad removes separately for added convenience
• Slim design fits 3 across in most mid-sized vehicles
• Dual flip-open cupholders
• Designed for longevity with up to a 10-year life span
• Ergonomic armrests are padded for extra comfort
• All-weather micro knit fabric provides all-season comfort
• Leatherette-wrapped calf support for comfort that grows with them
• Airline approved and FAA-certified for use in harness mode
• From fabric to foam and beyond, each element is smartly sourced to be both flame resistant and contain no added fire retardant chemicals
• Greenguard Gold certified 

Britax Grow With You ClickTight Features 

• SafeCells in base create crumple zone that absorbs crash energy
• Industrial strength steel frame
• Energy-absorbing chest pads
• Two layers of side impact protection
• Energy-absorbing v-shaped tether
• Features naturally flame-retardant fabrics without added flame-retardant chemicals
• Washer and dryer friendly-quick and easy cleanup with a removable cover
• Two cup and snack holders
• 9-position, quick-adjust harness and headrest
• Two position buckle can be moved outward to accommodate growing child
• Two recline positions
• Color-coded belt guides that make an easy install
• Stay-put, soft pads keep your child's neck from rubbing against harness strap
• Cool Flow model includes ventilated mesh fabrics along seat back
  

Comparing Specs and Dimensions: Nuna LUMN vs. Britax Grow With You ClickTight

The Nuna LUMN and Britax Grow With You ClickTight are similar in overall weight and recommended use. The LUMN is slightly more narrow making it a better fit for achieving three across or in smaller vehicles. The Britax Grow With You ClickTight has a higher headrest and higher harness slot point, which may make this the better seat if you have a taller child, especially one with a taller torso. 

Weight:

• Nuna LUMN: 26.2 lbs
• Britax Grow With You ClickTight: 25 lbs

Dimensions:

• Nuna LUMN: 23.5–26.25"L x 18.25"W x 25.5–32.5"H
• Britax Grow With You ClickTight: 21"L x 19"W x 25–35.5"H

Recommended Use:

• Nuna LUMN: 

Harness mode: 30–65 lbs; between 34" to 49" tall 
Booster mode: 40–110 lbs; between 43" to 63" tall

• Britax Grow With You ClickTight:

Harness mode: 25–65 lbs; between 34" to 49" tall 
Booster mode: 40–120 lbs; between 44" to 63" tall

Harness Height: 

• Nuna LUMN: 11" to 18.5"
• Britax Grow With You ClickTight: 12" to 20" 

Warranty:

• Nuna LUMN: Two years from original purchase date
• Britax Grow With You ClickTight: One year from original purchase date

Expiration:

• Nuna LUMN: 10 years from manufacture date
• Britax Grow With You ClickTight: 9 years from manufacture date

What seat is easier to install? Nuna LUMN vs. Britax Grow With You ClickTight

Nuna’s True Tension door and Britax’s ClickTight installation system serve essentially the same purpose: making car seat installation easier, faster, and more secure using the vehicle’s seat belt. 

• Nuna's True Tension door: It's a seat belt tensioning system where you route the belt, close the True Tension door, and it locks the seat belt tight. It ensures a solid install without a lot of tugging or wrestling with the belt.
• Britax's ClickTight: This is a patented system that opens up the seat base like a door. You simply route the seat belt through, buckle it, and then press the seat closed — which automatically tensions and locks the belt in place.

Both methods are essentially the same and are known for making seat belt installation virtually foolproof! No sweating, no stress, and no wondering if your seat is tight enough. 

What Seat Will Last Harnessed Longer? Nuna LUMN vs. Britax Grow With You ClickTight

To understand how long a car seat will last you need to know that car seats are outgrown by a few different factors. The most obvious being height and weight. However, there's a very important measurement that's often overlooked: harness height. When forward facing, the harness must come from above the shoulders or even with the shoulders. Once your child's shoulders go above the harness slot, the seat has been outgrown even if the overall height or weight of your child is within the seat's limits. As a reminder, when one limit has been reached, the car seat is outgrown.

Now in terms of these two car seats, the highest harness slot of the Britax is 20 inches. The highest harness slot of the Nuna LUMN is 18.5 inches. Therefore, the Britax Grow With You ClickTight will harness a child with a taller torso longer since the slot is higher. However, that doesn't mean you can't get the same use out of both seats. It really matters how a child's height is made up - maybe they have longer legs and thus they wouldn't outgrow the Nuna seat before the Britax. 

Therefore, there is not a clear answer here - it is really child dependent! 

Cleaning: Nuna LUMN vs. Britax Grow With You ClickTight

Cleaning either the Nuna LUMN or  Britax Grow With You ClickTight is pretty simple. You do have to remove the seat cover and pads, but both seats allow you to machine wash (gentle cycle) the fabrics with mild detergent. It's recommended to use cold water, rinse well, dry on flat surface, do not tumble dry, bleach, or dry-clean. One cleaning benefit for Britax is the SafeWash material is safe for BOTH the washer and dryer, making cleaning even easier!  

Note that the harnesses of the seats cannot be removed. When required the harnesses may be cleaned with a cloth with warm, soapy water. Never submerge the harness system or buckle. Towel dry any excess water and allow to air dry.

Never use bleach or harsh chemicals to clean any part of car seats.

Travel: Nuna LUMN vs. Britax Grow With You ClickTight

Since both the Nuna LUMN and Britax Grow With You ClickTight Harness to Booster seats are full-size, and on the heavier side, traveling with them may be a bit challenging, but definitely doable! Both seats are FAA approved in harness mode ONLY! Once your child is in booster mode and using the vehicle seat belt, they are not approved for use on the airplane itself (no boosters are approved in air crafts). 

The Nuna LUMN has the advantage here though since Nuna makes a dedicated travel bag for checking the car seat that comes with warranty! Nuna's Boarding Pass Program give families peace of mind by ensuring that their car seat is not only secure inside the travel bag, but also protected against any damage incurred during transit—Nuna will cover the cost of repair or replacement if damage occurs while packed in their bag.

If you are wanting a more compact, lighter travel seat, we would recommend traveling with the Way-B Pico if your child still needs a harness or the Cybex Solutions Booster seat if your child is in booster mode. 

What is the best harness to booster car seat? Nuna LUMN vs. Britax Grow With You ClickTight

The Nuna LUMN and Britax Grow With You ClickTight are standout choices from two of the most trusted names in child safety. Both seats offer advanced safety features, user-friendly installation systems, and premium materials—delivering top-tier protection and long-lasting comfort as your child grows.

Both seats are excellent choices for kids that are forward facing already, but may be needing a new seat due to handing their car seat down to a sibling, wanting to move to a "big kid" seat, or needing to purchase a new seat for a new vehicle. Both the LUMN and the Britax Grow With You ClickTight also offer extended harnessing as the highest harness slot is higher than many other seats. For example, the LUMN gives you more time harnessed than the Nuna EXEC as the harness is ??? inches higher (as long as your child still fits within the 49" max height/65 pounds max weight limit). 

Families looking to be more price-conscious are smart to consider the Britax Grow With You ClickTight Harness-2-Booster, as it comes in at about half the cost of the Nuna LUMN. Britax also offers two versions of the seat at different price points—the standard and the Plus. The Plus version is wider (22" wide) and includes an additional layer of side impact protection for enhanced safety.

For families prioritizing sleek, modern design that better matches their vehicle's aesthetics, the Nuna LUMN is a compelling option. With its premium materials, sophisticated styling, and luxury-level comfort features, the LUMN not only looks elevated but also feels like a high-end upgrade for your child’s ride.

Either way, when choosing between Britax and Nuna to protect your little one, you truly can’t go wrong.

Why should you trust Bambi Baby?

At Bambi Baby, our decades-long commitment to quality and customer satisfaction has established us as a trusted authority in the baby products' industry. With over 40 years of experience, we have developed a deep understanding of what parents require when choosing the perfect stroller. Our expert team is dedicated to guiding you through this important decision with personalized recommendations, ensuring that the stroller you pick perfectly matches your lifestyle and needs.

Still have questions? 

Bambi Baby experts are ready to connect! If you have any more questions regarding the Nuna LUMN and Britax Grow With You ClickTight Harness-2-Booster you can reach us at cs@bambibaby.com or chat with us on our website. We would love to hear from you!

We would also love to see you in store! Feel free to visit any of our store locations in New York, New Jersey, or Miami if you prefer personalized assistance from one of our experts. We're here to ensure you find the perfect gear for your baby with confidence and ease.