Ozone Therapy Machine - Buyers Guide)?

Hi. I would like to purchase an ozone therapy machine and might consider buying one second hand if that would save some money. I am new to this and unfamiliar with what I should be looking for to determine if a machine is one of good quality. I'd like to know what brands are good as well. I saw a few machines on Aliexpress. Should I stay clear of buying one direct from China? In the past, my luck has been hit and miss with other items I've ordered that way. The machines I'm seeing look identical to ones I've seen that can be purchased through a distributor here in the states. Are these knock off items?

Everything I can find online about buying a machine for personal use seems to be published by a machine manufacturer so I'm looking for unbiased info that will help me aquire a decent machine. Thank you for your help.