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I’ve installed all three of these Britax ClickTight convertible seats in my own vehicles, and the question I get most often is whether the extra money for the Advocate or Boulevard is worth it over the Marathon. The short answer: all three share the same steel-reinforced frame, the same ClickTight installation system, and the same 5-65 lb weight range. The real difference comes down to how many layers of side-impact protection you want and how much padding matters to you.
Here’s my hands-on breakdown of each model, what actually separates them, and which one makes the most sense for different families.
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Specs Compared: Marathon vs Advocate vs Boulevard
| Feature | Marathon | Advocate | Boulevard |
|---|---|---|---|
| Side Impact Protection | 1 layer (energy-absorbing shell) | 3 layers (shell + foam headrest + side cushions) | 2 layers (shell + foam headrest) |
| NHTSA Ease of Use (RF) | 5 stars | 5 stars | 4 stars |
| NHTSA Ease of Use (FF) | 5 stars | 5 stars | 5 stars |
| Weight | 28.5 lbs | 30.6 lbs | 29.4 lbs |
| Width | 18.5 inches | 20.5 inches | 18.5 inches |
| Rear-Facing Weight | 5-40 lbs | 5-40 lbs | 5-40 lbs |
| Forward-Facing Weight | 20-65 lbs | 20-65 lbs | 20-65 lbs |
| Height Limit | 49 inches | 49 inches | 49 inches |
| Harness Positions | 14-position, no-rethread | 14-position, no-rethread | 14-position, no-rethread |
| ClickTight Installation | Yes | Yes | Yes |
| Steel Frame | Yes | Yes | Yes |
| Impact-Absorbing Base | Yes | Yes | Yes |
| Machine-Washable Cover | Yes | Yes | Yes |
| Infant Insert | Included | Included | Included |
What All Three Share
Before getting into the differences, it’s worth noting how much these three seats have in common — because it’s a lot.
All three use Britax’s ClickTight installation system, which is the easiest belt-installation method I’ve used on any car seat. You lift a panel on the front of the seat, route the seat belt through, and close the panel. That’s it. No wrestling with LATCH straps, no knee-in-the-seat tightening. The seat belt locks automatically and the installation is rock-solid every time.
All three also share the same SafeCell impact-absorbing base (it compresses to absorb crash energy), a steel-reinforced frame, a patented V-shaped tether that reduces forward rotation in a crash, a 14-position no-rethread harness, 7 recline angles, and a 10-year expiration. The weight range is identical across all three: 5-40 lbs rear-facing and 20-65 lbs forward-facing.
So if the frame, installation, harness, and weight limits are identical, what’s actually different?
The Real Difference: Side Impact Protection Layers
The main distinction between these three seats is the number of side-impact protection layers, which affects both the price and the width of the seat.
The Marathon has one layer: Britax’s deep energy-absorbing shell (SafeCell). This is the same shell technology used on all three, and on its own it provides solid side-impact protection. The Marathon is the narrowest at 18.5 inches and the lightest at 28.5 lbs, which makes it the best choice for three-across installations or smaller vehicles.
The Boulevard adds a second layer: a foam-lined headrest that provides additional head and neck protection. At 18.5 inches wide and 29.4 lbs, it’s the same width as the Marathon but about a pound heavier. This is the sweet spot for most families — meaningful added protection without the extra bulk.
The Advocate goes to three layers: the shell, the foam headrest, and external side cushions. This gives it the most comprehensive side-impact protection in the lineup, but it’s also the widest at 20.5 inches and heaviest at 30.6 lbs. Those extra 2 inches of width can matter in tight back seats.
Britax Marathon ClickTight
The Marathon is Britax’s entry point into the ClickTight lineup, and it’s a genuinely excellent car seat in its own right. The single-layer SafeCell protection passed every crash test with strong results, and the 5-star NHTSA ease-of-use rating in both directions confirms what I found in practice: this seat is straightforward to install and adjust.
I particularly like the Marathon for families who need to move the seat between vehicles regularly. At 28.5 lbs it’s not light by any means, but it’s the lightest of the three, and the ClickTight system means reinstallation takes about 60 seconds. The 7 recline angles and automatic level indicator make it easy to get the right angle for any age.
The main trade-off is padding — the Marathon has adequate cushioning but noticeably less than the Boulevard or Advocate. For long road trips, your child might be more comfortable in one of the more padded options.
Best for: Families who want ClickTight quality at the lowest price point, need to fit three seats across, or frequently move the seat between vehicles.
Check Marathon prices on Amazon
Britax Advocate ClickTight
The Advocate is the safety flagship of the ClickTight line with three layers of side-impact protection. In my hands-on testing, the external side cushions give it a noticeably more padded feel around the head and torso area compared to the Marathon and Boulevard. If maximum side-impact protection is your top priority, this is the seat.
The trade-off is width. At 20.5 inches, the Advocate is 2 inches wider than both the Marathon and Boulevard, which rules it out for most three-across setups. It’s also the heaviest at 30.6 lbs — not a deal-breaker, but something to consider if you move the seat between cars regularly.
One thing that surprised me: despite having the most protection layers, the Advocate has historically been priced between the Marathon and Boulevard rather than at the top. The Boulevard’s premium pricing comes from its extra padding and comfort features rather than raw safety layers.
Best for: Families with plenty of back seat space who want the maximum side-impact protection available in a convertible seat.
Check Advocate prices on Amazon
Britax Boulevard ClickTight
The Boulevard sits in the middle for protection (two layers) but at the top for comfort and overall refinement. The foam-lined headrest adds genuine head and neck protection beyond what the Marathon offers, and the padding throughout the seat is noticeably plush. At 18.5 inches wide, it maintains the same narrow profile as the Marathon — giving you better protection than the Marathon without the width penalty of the Advocate.
I’ve recommended the Boulevard more than any other Britax ClickTight because it represents the best balance of protection, comfort, and practicality. The 4-star NHTSA ease-of-use rating for rear-facing (versus 5 stars for the Marathon) is a minor ding that I didn’t notice in practice — installation felt equally straightforward across all three.
The Boulevard is typically the most expensive of the three, which reflects its premium padding and materials rather than a safety advantage over the Advocate.
Best for: Families who want the best combination of enhanced protection and a narrow profile, and don’t mind paying a premium for comfort.
Check Boulevard prices on Amazon
Which One Should You Buy?
All three of these seats provide excellent crash protection thanks to the shared SafeCell technology, steel frame, and ClickTight installation. You genuinely can’t go wrong with any of them. Here’s how I’d decide:
Choose the Marathon if you want the best value, need the lightest option for moving between vehicles, or are doing a three-across setup where every inch matters.
Choose the Boulevard if you want enhanced head and neck protection with premium comfort and can keep the narrow 18.5-inch width. This is my default recommendation for most families.
Choose the Advocate if maximum side-impact protection is your priority and you have the back seat space for its 20.5-inch width.
Whichever you choose, all three are compatible with the Britax anti-rebound bar (sold separately), which adds additional rear-facing crash protection. For more Britax options, see our full Britax convertible car seat guide, or check our overall best-rated convertible car seats for cross-brand comparisons.
