The "Princess" element went down rather well with our 3 year old, which is why we bought it, however, in use the seat is really prone to slipping out of place or tipping over.
We have a Volvo S40 with leather seats which are fairly flat, and a Vauxhall Corsa with cloth seats which are also quite flat. The base of the booster seat is very narrow, so every time my daughter tries to sit on it it tips over. the gap between the "horns" and the seat is also wide, so the seatbelt provides little stability. It wobbles & slips quite a bit in use.
It might fit better on a car with more contoured seats, but I suspect we've paid more to disney for the princesses, than we did for the design & manufacture of the seat.