There are many different opinions on wheel covers and whether or not they are safe and cleanly. Personally, I love wheel covers. I've heard so many times over that wheel covers are dangerous, cause urine burn, snagged nails, etc. Usually I see these things in hedgehog Facebook groups that are run by people that aren't breeders and have never tried out a wheel cover for themselves. I have been using covers for years with many hedgehogs and would like to share my experience with them.
Lets start with whether or not they are cleanly. Wheel covers will wick away urine while the hedgehog is running and their feces will ball up and roll off the wheel. That sentence alone should answer that question. I find that wheel covers are much cleanlier than a wheel without one.
If you've ever owned a hedgehog, you've seen what a non-covered wheel looks like after a whole night of running. Its not a pretty sight! Wheels without covers will be caked with urine and feces. Some of the urine will run off while the wheel is turning but since the feces just gets trampled all over the wheel, most of the urine does too and it becomes a muddy mess. When they run for hours in their own poop and urine, the feces starts to cake onto the hedgehogs feet (often adorably referred to as poop boots).
When wheels have fleece covers, the moisture is absorbed and wicked away from the hedgehogs feet. Yes, eventually a wheel cover will get saturated in urine. That's when its time to throw it in the wash! If you don't clean your covers regularly, of course it could cause urine burn. Urine burn can also happen from cages that aren't cleaned regularly. It's important to any animals health to keep their living space clean. I recommend cleaning cages at least weekly. I wash all of my covers every 5-7 days. Some hedgehogs are messier than others and a cover may need to be washed more often. I have NEVER had a case of urine burned feet, because I wash my covers when they are dirty.
As for the feces, it almost never sticks to the wheel cover because the urine is wicked away and the cover wont be wet like a non-covered wheel. Poop boots can still happen but definitely not as frequently.
The other issue I see discussed are that wheel covers can cause snagged nails and are therefor dangerous. This one boggles my mind because most consider fleece bedding a safe option. Hedgehogs run around their cages as well, so why would fleece only be dangerous when on a wheel cover? Wheel covers are literally made with the same fleeces used as bedding which are blizzard and anti-pill fleeces.
I've been using wheel covers for about 4-5 years and have never had a snagged nail. I don't doubt that a snagged nail could happen if the hedgehogs nails aren't trimmed regularly, but the same goes for fleece bedding.
Lastly my favorite thing I hear, "Wheel covers are for lazy people. Just wash your wheel!". My wheel cleaning day consists of removing the covers and shaking them out (because I use pine shavings for bedding, which sticks to the fleece), putting them in the washer on a double rinse cycle, shake out the clean wheel covers into the washing machine to remove the remaining shavings, throw them in the dryer, vacuum the shaving out of the washing machine, wash the actual wheels with hot soapy water, then add a clean wheel cover to the clean wheel.
If I didn't use wheel covers, I would soak the wheels and wipe the feces away with a scrub sponge. Which of course is also hard work, gross and not fun to do, but its definitely not quicker or easier than the ritual that I do every week.
Do I think wheel covers are better than a non-covered wheel? Absolutely not.
Do I think its cleanlier to have wheel covers? Absolutely.
Do I think that everyone needs to use a wheel cover? Definitely not.
Do wheel covers cause urine burn? Nope, not if they cages are cleaned properly.
Do wheel covers cause snagged nails? Not if they are trimmed regularly.
It all comes down to preference! Personally, the cleaner feet is the winner for me!