You could buy a used Onkyo changer, or you can take your chances with the one that is new. Of course, used is also somewhat risky, as there is no guarantee with it. If you choose to take your chances with a new one, I strongly recommend buying from some store that has a superb return policy (including them paying return shipping, if it is not a local store) and that would not be too inconvenient for you to return it to them, if it turns out to be problematic.
As for changers in general, I don't think that carousel changers tend to be significantly different in reliability than single disc players, due to them having only a very simple additional mechanism that simply moves the discs in a circle. And from reading about this issue in the past, and from my brother who repairs electronics for a living. And from my personal experience with them, which is too small of a sample size to infer anything much in itself, but my personal experience fits in with all of the other information I have encountered regarding this matter.
Other types of changers tend to be less reliable, and more likely to damage discs if things go wrong. This I know from sources like Consumer Reports and my electronics technician brother.
If the new Onkyo changer is unreliable, it means that Onkyo screwed something up horribly, as carousel CD changers tend to be very reliable, just like single disc players tend to be very reliable. Of course, eventually, they will die, but they typically last a long time if not abused.
I have an old Onkyo DX-C340, which must be about 10 years old or so, and it works beautifully. If it died now, that would not be too bad of a run for such a player, but it is not showing any signs of dying. When it eventually does die, I will be sad if my only choice is the DX-C390 or a different brand that only holds 5 discs. Maybe I should start haunting thrift stores for very cheap used Onkyo changers that are no older than my current one...