Comment by MrMcCall
Thankfully, none of us has had asthma. As far as anecdata:
The device does have a what-appears-to-be-accurate AQ (air quality) sensor on the side. In the presence of smoke, it turns red, cranks itself up, and then returns to blue (clearest) through purple over the course of some minutes. As such, I'd say that the "response curves" looked legit to my programmer brain, besides that the air certainly smells better.
I can definitely say, however, that -- having replaced the filters three times over these four years -- the HEPA layer (the inmost) definitely got brownish. Each 3-6 month pre-filter cleaning cycle had nice gradations of dust and stuff after each cleaning, sometimes a great deal if we were slacking.
Regardless, who knows what's been sucked into and blown through our ancient HVAC unit's ducts over these past decades, what with most people probably just buying the cheapest air filter possible? Why not err on the side of caution w/rt AQ?
Interesting point. I have $cheap brand air purifiers, and the filters never get that dirty—but we have radiant heating in the floors and no AC, so no ducts, so maybe that’s why?