ok for one thing co2 barely has a smell if you can smell it in your house your burning it for far too long and id say the same with your friend. another thing i dont think ozonators are bad for plants they help keep bacteria in the air kept to a minimum and yes they are harmful to ppl just shut it off when you go in the room now for the co2 burner itself i will depend if your burning propane or natural gas to create your co2
one may smell more than the other i havent been able to notice maybe im just used to it but i doubt it nobody ever asks me whats that smell when i have ppl over so my guess is they are running it for far too long i have all the gadgets as well and what i use is a light sensor/timer you can set it for how long to run for and set the frequency that it comes on in my room i run it for 12 minutes on out of every 30 minutesso 12 on 18 off but it will vary depending on your room size if you ask me if you dont know what your doing i wouldnt bother messin with it lol newb