Works - Had it for years
I'm not sure why previous reviews state it doesn't work.  I've had my unit for years, and with proper filter replacement (I do it twice a year due to SEVERE allergies) it definitely makes a difference.  My allergies have gotten so severe that the physician has finally given me an epi pen.  I sleep with it at night on 2 or 3 and it is loud, but we use it as white noise.  The 1st setting is very quiet.  We had all the fires around us recently and the filter clearly worked as the filter was black.  We let one of our friend's mother borrow one unit as she was having problems breathing.  It helped her and cleared their little apartment of the smoke!  So much so she went out to purchase one.
Rating: 5 stars