Bought two of these last round and I believe they work fairly well. At first I wasn't sure as it stayed blue most the time so I couldn't figure out if we just have fairly clean air or it just wasn't working, but during a deep clean day of dusting the light on front went red quickly after I started dusting in the room and it went into high mode automatically and ran for a while through it's light indicator until it hit blue again. I noticed it does change the air quality indicator when we are stirring up things in the room. Our air runs 15-18 hours a day in the summer and I use high micron filters anyway, so our air might be fairly clear for the most part, but it's nice having these help give an extra scrub in the rooms the dog and our child stay in.
Only complaint so far is the night time mode turns off all lights but one...and that one light is bright enough to light up a corner (I like pitch black when sleeping), so I put tape over that light.