In one dept at work, a lady has some allergy, so she has to run this 'air purifier'. I went in there to do some work, and my eyes started burning. The ozone smell was awful. I told them that ozone is bad for you when it's this strong, and ozone is one of the bad components of smog. Later when I had some time, I did a web search for ozone and air purifiers, and I found that some of these supposedly air purifiers put out way too much ozone and pollute tha air. I suggest you check those out to find out more about the bad effects of breathing ozone.
As for piezo transformers, they seem to be a cheaper way of doing what has been done for more than a hundred years, with simply a lot of very thin wire and some iron for the core to wind it on. You can make tens of thousands of volts with a flyback and tripler.
Also some sellers make claims about their products that are unsubstantiated, such as their effectiveness in a large area. If you use one of these small devices in a small closed room, they may be effective, but if they're in a cubicle in a large room, it's doubtful they can be of any halp.