I have to say, the lack of cupholders and the 40 lb. limit are the 2 things stopping me from buying one.
I have an almost-6-year old who is THAT close to 40, but she can't seem to gain that last 1/2 lb. And the way she is, I know if she does hit 40 in the next month, she could drop back down to 37 at any time. She's not getting one because while it would be a SMIDGE easier to buckle than the Turbo in our car, the 40 lb. limit means she'd often be under the limit-- which honestly I'd be comfortable with except for the setting a bad example thing-- and she does like the cup holder on the Turbo.
I think Britax would do better to lower the weight limit to 33 or 35, and put an age limit on it (4 years, 5 years, whatever) that means kids who are lighter at an older age can get the anti-submarine benefit of this booster! I mean, seriously, we know that's a greater risk for under 40 lbs.-- why deny that benefit to kids under 40 lbs.?