Bought the 211+ after reviewing a consumer magazine.  The Blue product was rated much higher than other brands I was more familiar with and decided to give it a try.  Completely changed our large room!  The room feels and smells cleaner! The unit is very quiet.  We notice less dust particles in the air and even our dog's allergies have improved. It performed amazingly during our heavy pollen season!  Looking to buy another smaller unit for our bedroom.