The feature which sets them apart from the competition is that while still being solidy built, they are not unnessesarily bulky, especially in the base, which means an adult can still sit comforably between two of them in the back seat of the car.
The seats are very well built so if I look after them, I expect to be able to sell these in a few years' time through a site like Pre-Loved and get most of my money back.