I have used those wheels for about 8 years now and have never had any injuries. I have about 200 adult chinchillas that use them and I produce over one hundred babies a year that start using them at 8 weeks of age. I do make sure they are 6 inches away from the cage wall if there are more than 2 chinchillas in the cage, so one chinchilla can't crawl up the side while another is running on it. The wire mesh is a tiny bit larger than 1/8" square. I know many people are against this wheel and we have already had a debate on CnH about it so, I won't debate it again, but I have to go with my experience with this wheel and it has been 100% positive. I do wish it was larger than the 11" in diameter because I breed very large chinchillas. I am in the works with a sheet metal company to try and produce the larger 14" in diameter sheet metal wheel with a solid side at a more affordable price and am waiting to hear back from him. If he is able to make that wheel, I would buy them wholesale and would ultimately like to use all of that style instead.