I read hundreds of reviews and looked at several other competing brands. I went with Alen because of the good reviews. I purchased 5 units for 5 different rooms. Honestly, I was expecting to notice some difference but I can not tell any difference in any of the rooms. My daughter says she has noticed a difference and does not have watery eyes and is not sneezing in her room. She also says the dust in her room is less. The dust accumulation in my room has not seemed to change any.