I believe they are useful, and good. Just that one needs to be aware of, and build around, their inherent dangers. Gasoline is a good, useful thing, and can be used and stored safely. Same applies here. Just use ones head when designing a system. To me, it seems like a great addition to an existing ventilation system. The only variable that would need to be found is how much moving air can they clean CFM wise without flowing air past them too fast to be cleaned, and adjust the CFM rate accordingly. The other option is to vent into a box (large dog house, under an enclosed porch, etc) Hang one or two in there, and let the clean air just flow out small vents. All ya want to do is avoid any high concentrations of O3 accumulating in an area that might spark, or that you would have some extended exposure to.
I don't worry about the smell in the house. The exhaust creates a negative pressure in the grow room. It's the vent OUTLET ya gotta worry about. I am torn between venting down the main sewer pipe, or a couple of these under the back porch enclosed area.

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You can lead a Horticulture....But you can't make her think!!!!