I received a Medium Room Air purifier in exchange for my honest review.  I was extremely excited to use this purifier and immediately un-boxed and started up.  It was extremely quite with just a faint whisper even at its highest setting.  I did not detect a change in the air quality right away, but after a week the air seemed fresher.  It has an electrostatic feature, which I honestly could not tell the difference between on and off.  I also shudder to think of the replacement costs for the filters.