I expected a high-quality air purifier from Alen and wasn't disappointed. I bought this model because we live in a new neighborhood with lots of construction going on all around us. We end up with a lot of dirt and dust making its way inside our home. Although our air quality was pretty bad, it took only a few hours for the monitor to go from red to blue. My husband even commented on how much better the air is now when you walk into our house. My only regret is that I didn't buy it sooner.