[Zalea]

Many people put a litter box under the wheel to catch any run-off from it. My little one likes to go in a certain corner of the cage, so I just put a paper towel down in that area. I would stay away from anything that smells or has crystals in it. A slight scent to you can be overwhelming for them and I'd be afraid there would be something bad in the crystals if eaten--not to mention a choking hazard. Honestly I usually just tell people to use a paper towel because they're cheap and do the job without any huge worries. Others might have a different opinion for you though.

Do keep in mind, they litter train you basically. You put the pan where they want to go and if they want to use it they will. If not they won't.