A 20x20 fan DIY was actually on my todo list. This is the first time I've seen a box with multiple filters on it, however -- all the ones I saw before just taped a single filter to the fan. Are the multiple filters a big practical improvement?

(I used to own an expensive air filter that was top-rated by Consumer Reports at the time, but sold it during a minimalism phase. Now I want to try a filter again, this pollen season, but more frugally.)