I was a user of ONA gel. closet grow, 3' x 5' vented into a bathroom with an open window. I had a jar of ONA Pro Gel and a bottle of the liquid to reconstitute the gel. (the gel will last sooo much longer that way). At first, it totally masked the smell of weed, however the entire house had that ONA smell. About 2-3 weeks into using it, I'm beginning to smell the marijuana vaguely, almost hidden by the ONA, but definetly smelling a fresh plant. Half way through flowering, I realized I was becoming accustomed to the ONA and was able to discern the weed again. Even my roommate made the same comment.
I Highly recommend ONA on hand for sudden visits from family or friends that are unannounced. Pop that jar open asap and no worries. For full time protection, I have a scrubber in my tent AND an ozone generator not far from the grow room door. The tent has negative air pressure, so all odor is scrubbed through the can filter before leaving the tent. The ozone generator kills any smells that escape when I open the tent door.
For those that are growing in a closet or small space, consider getting an ozone generator. (about $70 on eBay) Not only does it kill odor, ozone is beneficial to plants as is the co2 generated. ONA can't do that. But as I said, do keep ONA on hand for emergencies or even planned events, like Thanksgiving dinner with the inlaws. They may wonder why your house smells hospital clean, but they won't smell weed the short time they are there. (The odor is there however!! ONA does not negate weed odor, it just masks it. Keep that in mind)