@suetanvil@freeradical.zone Personally, I still prefer the original DIY 4-filter design, as it shows better filtration performance when using the same number of fans: https://www.texairfilters.com/comparing-the-performance-of-corsi-rosenthal-boxes-made-with-box-fans-and-pc-fans/ However, the Clean Air Kits tend to have more fans to offset this while maintaining a slimmer footprint. Both methods are solid performers, and it largely comes down to preference/priorities. Things like footprint, ease of filter replacement, aesthetics, etc.