Contrary to other reviews, the hamster stabiliser does stay on our hamsters and they rarely flip over (tried it on at least 3 different ones). It is true that you have to press the button on the back of the hamster and quickly close the lid to the ball. But I haven't had any difficulty. Just have to be quick about it :-). I have 6 hamsters, 2 room house, runway, and ball. My kids play with these for about 15-30 minutes once or twice a day. I wish they would be entertained by them longer. And I wish the batteries lasted longer too!