I bought an Ozonics unit last year. I'd say Dan Johnson from Nine Finger Chronicles podcast was the one who finally convinced me to spend the cash. He interviewed a guy who basically said that the Ozonics unit did such a good job at reducing his scent and allowing close encounters with deer, that he would buy a new one every year if he had to. Thankfully, they last a lot longer than a year!
I used mine for maybe 10 days of hunting last year. I never had a deer blow at me while I had it turned on. I had deer pass downwind inside of bow range, and they could sometimes tell something was up, but they never got so spooked that they blew at me. In fact, they never altered their direction of travel. One buck simply skirted around me at 30 yards instead of staying on the trail that would have put him inside of 10 yards from my tree. I still don't have enough experience with my Ozonics to say how MUCH of a difference it makes, but I feel confident that it definitely helps and does a better job than scent free spray, detergent, etc.