People say they have no problem with the vertical wheel ones, but I decided to play it safe and built the Ikea wheel, it's horizontal, aka flying saucer style. Overall, I think it's actually CHEAPER to build your own, Popsicle absolutely loves his wheel, and I didn't follow the instructions just made it by using industrial glue to stick the lazy susan onto some inclined pieces of wood, so it was very low effort.
Overall, people are ALWAYS posting on this board about chinchilla health problems, and not one person has posted about the wheel causing back problems. So it seems PRETTY safe.