Silent Spinners are not safe.
1. They are made of two pieces and there is a joint all around the center running tread where the two pieces meet. Not only is there a joint but there are slits there to let urine drain. Both the joint and the slits can catch little toes and nails while running and cause injury.
People have tried to solve this problem by putting tape over the joint and drainage slits but then the urine can't drain out so they run in the urine. Of course tape on a running surface is always a risk.
2. There is a nut both front and back and both those nuts are known to come undone causing the wheel to fall.
3. The wheel extends out past the metal frame. When a hedgehog enters or exits, especially a larger hedgie, the wheel can tip over on the hedgie.
The wheel itself is made of brittle plastic and can crack fairly easily.
If you want to buy a commercially made wheel, go with the giant Comfort wheel.