Yes they're good
I have one on a shelf and used to have one on top of a flat-roofed house. As Cypher says they're too heavy to sit on substrate as they could squash the hammy if they dug underneath it. You can also use a small terracotta plant pot, or a plant pot saucer or a ceramic mug, and put them in the fridge, then put them in the cage about the time they wake up. I used to have two to rotate so one was always in the fridge.