Rotastak wheels are too small for a fully grown Syrian and a correctly-sized wheel does not fit anywhere in the set up. For that fact alone, they are unsuitable... that's without even going into the problem of lack of corners (which hamsters love) and hamsters getting stuck in the tubes. I'm sure plenty of hamster look happy in them, but they've never known anything else. Hamsters make the best of what they have. They can't exactly tell you if they don't like something. They can't say "excuse me, i'd like my cage to have corners, please"
