Glides work for both carpet and Hardfloors. We do recomend them for hard floors as they don't move around. (even when locked rollers have a tendency to move some on hard floors.)
Rollers are great for carpeted floors and make rearanging the bed room a breeze! (Even when locked, Rollers have a tendency to move some when on hard floors.)
Either option is the same low price. and they both have 7.5 inches from the floor to the bottom of the mattress.