DS2 (9 yrs., 54" tall, 90 lbs.) is the perfect size for this product and he tested it extensively in the first few weeks that we had it. He said that even though it's firm that his "butt forgot about it after a few minutes". I laughed about that comment but I totally understand it too. When you sit on it and someone asks for your opinion - your brain is focused on how it feels compared with what you're used to. But after a few minutes of driving around you forget about it being there and it's fine.
Now, granted, he's a big kid and he is at that "in between" stage where most boosters are too small but the seatbelt in our vehicles doesn't fit him right yet. The Incognito is a perfect fit for him and he's a big fan because he's a smart, cps-savvy kid who understands and appreciates the niche that Dorel is trying to fill with this product. I think if they sent us 300 of them my son would be very happy to hand them out and sing their praises to every kid in the 4th grade. Lol.
FWIW - the Recaro Performance Sport on the seat next to him didn't fit him. I had to stuff him into it (and bribe him to smile) just for a few pictures.