"keep in mind that the cheapest and most expensive seats must meet the exact same safety ratings in order to be sold."
While this is true...it doesn't really tell the whole story.
With my first daughter, due to finances, we had a Cosco convertible seat--easily the cheapest seat on the market at the time. And I routinely cut myself on the sharp plastic when I was installing it. The straps got twisty REALLY easily, and the rear tether was such a PIA to use.
Later I got a Fisher Price Safe Embrace (no longer made, it was at the time the "second favorite" seat for certified techs, with Britax pulling the lead). "Same safety ratings." But it added in energy absorbing foam (the stuff bike helmets are made of) for protection against side impact crashes. Testing in America does not include side impact even though half of all child deaths in crashes are from side impact crashes! European regulations require side impact protection, and all of their seats require energy absorbing foam. The straps were made of the same webbing that vehicle belts are made of...and just did NOT twist. The tether was super easy to use. Built in locking clips (better than the Britax built in clips), so no more fussing with those little "I" clips. Not a sharp edge to be found. The difference in safety provided by this seat was really easy to see.
Another thing on the *mininum* guidelines...American regulations do not require that chest forces be measured in car seat tests. European regulations do. In Europe "overhead shield" style seats are not sold because they create too much chest force. Kids are literally expected to slam against that bar, and may end up with broken ribs, arms, jaws... Similarly, overhead shield seats do not perform as well in side impact crashes as 5 point harness styles do. When I was a certified tech I would tell people to only use overhead shields if it was the only way they were going to properly buckle a child in (because admittedly, they are a tiny bit easier to use than 5 point seats).
Britax seats were originally designed for the European market, so they meet both European and American standards. I don't have any Britax seats because I just can't afford them (my youngest son who is 4 is in an Evenflo Triumph, older three kids are all in boosters). But just because all seats must meet a "minimum" safety threshold does not mean that they are all created equal.