Are you talking about not staying in a ready bed? I was really surprised that Holly ever stayed in hers, she was such a mobile sleeper too, she'd be upside down and turned around in her cot, but she never moves in her ready bed. they smaller ones have slightly raised sides to help with this.
They re noisy though! If you blow them up too much they squeak like hell! Most of the people I know (loads on here) who have got them love them to pieces but my godson can not sleep on one at all, he ended up in his mum and dads bed this weekend when they were with us, his dad slept in the redy bed!!!!