I'm aware of how it works. It is an ozone generator likely left next to the CPAP (even in their own product literature) that leaves ozone inside the CPAP tube and machine, while polluting the area/room with increased levels.

You're essentially taking people with breathing difficulties and increasing their exposure to a substance that is known at low levels to cause breathing problems. Additionally CPAP's filter systems have no way of removing O3 from the room's air.

When properly used the device is harmful.

The crux of it, I'd say, is that it ought to be regulated as a medical device, and the manufacturer ought to be required to prove it is safe. If it leaves any form of residue or serves a medical purpose in using it on a medical device, it ought to be regulated in the same way. (Comet can't be sold as an insulin needle cleaner, either.)

Not that medical devices aren't themselves the Wild West. Hip replacements? We used those without testing for decades. CPAP? Technically only available by prescription, but go on eBay and you can order what you like.

Our regulatory authorities in the U.S. are a real mess. And while I believe we can trust Americans not to poop where they sleep (i.e. knowingly sell lead contaminated products to their neighbors), it makes no difference if our addiction to cheap Asian imports means we get products from people who don't feel much distress if someone in a faraway country gets sick (and can't be arrested for making them sick, either, since there functionally no truly international law enforcement).