I had plans to do proper measurement of the how well these things actually clean compared to a traditional box fan CR box, and the Airmega devices (especially after someone on here argued w/ me that they couldn't possibly work, lol). But life got in the way, so I haven't. However, my air monitors are telling me that they work, so I'll keep using them. I really need to build a 3rd one, as a matter of fact. I used the filters for about 18-21 months before replacing them.