I have heard from others that the Longevity saunas smell bad at first. Ozone will take care of the smell. Maybe you should just run the unit with the ozone on a few times without being in it. Keep the o2 flow very slow so that the concentration of ozone will be high. When you use the unit, keep the concentration high as well. 28 to 40 gamma is ideal.
Sniffing the top of a jar of freshly ozonated water is just about as bad as sticking the output tube in your mouth and inhaling deeply. It will hurt a lot and cause uncontrollable coughing, but IMHO there will be no permanent damage. I have mistakenly inhaled ozone 500,000 times more concentrated than the EPA tells me is safe and I'm here to tell the story. I also think I purged my lungs of 20 years of smoking in the process. It was not fun and I would not recommend it to anyone, but now I can tolerate greater amounts of ozone.
I would attempt to seal the unit better with the addition of self-adhesive weather stripping and use a towel around your neck while in the sauna. The cost of an extra concentrator or tank/regulator is a bit prohibitive.
Although I was never seriously ill, I have not had so much as a cold for over ten years. I guess that's a benefit. I don't even use our sauna tent that much anymore. I prefer the ozonated hot tub instead, especially in the winter here in Canada.
Hope this helps,