Comment by Rebelgecko

Compared to a dedicated air purifier, a box fan one is louder, has higher energy consumption, and is uglier (I suppose the last one is subjective).

If it's something you only use a couple days a year when your region is on fire, then absolutely go with the design with lower upfront costs. But if you're running it 24/7, it's worth thinking about the extra 40-80 watts that a box fan uses.

For me, I figure the electricity difference comes out to around $100/yr so getting a dedicated air purifier has paid for itself (although I live in an area with fairly expensive electricity). It also has some nice bonuses compared to a box fan like auto adjusting speeds and a prefilter that hopefully helps the "real" filter last longer.