They work okay as long as there is sufficient grip either from tightness of the fit, or through friction. For example, i tried putting a stainless bottle in a plastic cage and it bounced out while going over some bumps. But I got a rubber coated cage that was a little smaller in diameter, and I haven't had the bottle move at all. Also tried a tighter fitting plastic bottle in the plastic cage and no problems there either. Another option is the Two Fish velcro mount cage that you can put on your handlepost.