This is actually the third model of Britax car seat I've owned and reviewed. Previous to the Advocate CS, I had a brief period with the
Britax Decathlon before buying a second
Britax Boulevard.
The Advocate CS is very, very similar to the Boulevard in just about every regard.
From the very top, the headrest is easily moved up and down by turning a knob on the side of the seat. Once this is installed, you probably won't have to take it out of your car, other than turning it from rear-facing to front-facing, and when your child is finally too big for it. Having dealt with the "put three straps on this weird clip thing" seats, you will never, EVER want to go back after you've used the adjustment knob.
The padding is every bit as good as what you'd find on a Boulevard (and a step up from the lower-tier models, in my opinion). The fabric is made very well made and has a somewhat dense feel to it, but at the same time, it breathes well, so your child won't get too hot in warmer temperatures.
The tether system is basically unchanged from the Boulevard. There are nice, soft color-matched shoulder pads, followed by a non-slip chest harness that somehow manages to stay in place without "sticking" to your child. The Click & Safe adjustment strap is of somewhat questionable value to me. When you tug the bottom strap to tighten the harness, you hear a noise almost like a ratchet when it's snug enough. That's great if you're not used to putting your child in a seat, but in my experience, finding the proper snugness isn't very difficult. For me, the clicking was consistent with the tightness I would have used anyway. Obviously, this is something that's going to vary by the individual (and whoever else may be using their seat). Is it a good feature? Absolutely. Would I opt for a less expensive non-CS version of the Advocate (vis a vis the Boulevard and Boulevard CS)? More likely than not.
Actually installing the seat is pretty straightforward. Just like the Boulevard, the LATCH straps are mounted to an independent steel bar. Much like the headrest, this is an excellent feature that you will instantly miss if you ever have to use a child seat that isn't designed this way. Installation for experienced parents takes about two minutes. New parents... I'd give it five. Ten if you count having someone come and make sure you did it right. (No shame. I used to be guilty of this myself.) The top LATCH connector is similarly easy, and as with the Boulevard, the Advocate comes with a nice pouch for storing the tether and / or slack from it.
While the Boulevard is a relatively large child seat, the Advocate CS is a monstrosity. If you look closely at the picture, the off-white hump on the back is actually one of the two plastic side impact "wings" in addition to the cushion wings on the seat. While I like that Britax seems to be taking a "more is more" approach to impact protection, those plastic wings are not only big, they're not even sort of color-matched.
"Color matched? WHY DO YOU CARE ABOUT THAT? YOU ARE AN AWFUL PARENT! SHAME ON YOU!" Okay, let's level with each other here. We're talking about an unusually expensive child seat with replaceable fabric covers that cost nearly as much as buying a whole new child seat from another company. Yes, you're paying for safety, but you're also paying for a certain amount of cachet. So, when you buy yourself an Onyx or Opus Gray Advocate CS expecting it to match your black interior, understand that you're going to have huge white plastic wings, too.
More importantly than color though, is the real value of the side wings -- which, like so many other things, depends on your personal situation. The wings are designed for two main purposes: 1) Additional protection of your child, in the event a side impact is severe enough to cause the interior of your car to make physical contact with the seat and 2) Protection for rear passengers who may be thrown or pushed against the seat in the event of an impact.
For my personal situation, we have one child, whose seat is positioned in the center of the rear seat. There's nobody else back there to be hurt by the child seat, and if an impact is severe enough for the interior to make contact with the seat, the accident would almost certainly be fatal for all passengers, regardless. On the other hand... If I regularly had passengers who sat in the back seat such that there was someone else who could potentially be injured, and I had to put the seat near one of the side doors, I would not hesitate to buy the Advocate precisely for the added protection. Seriously. When you're looking at this much money for a child seat, what's an extra $40?
So... would I recommend it? To many people, without question. Sure, some things border on gimmicky, but I can't think of a safer seat you can buy. That said, if money's a concern, if you don't have other back seat passengers, or if you're concerned about appearance almost as much as safety, I really think the Boulevard may be a better choice. If you have your heart set on Click & Safe, maybe the
Boulevard CS. If you took off the side plastic wings from the Advocate CS, you'd have a Boulevard CS. At the end of the day, all three are incredibly well-built seats that are packed with features, and better than "comfortable" for your child.