I decided to try this air purifier because my house is always dusty regardless of how often I vacuum or dust.  I've been using it in my living room and have it set to auto. I was disappointed at first that in my house auto equaled it was running all the time, so I decided to turn it off for a bit. What I noticed is that the dust on the entertainment stand was back within a short time after I stopped running the machine, what this told me is that the machine was correct to be running as often as it was. 

Overall, I'm very pleased with the the air purifier and would recommend it to others. It has a lot of settings, but I choose to continue to use the "auto" feature.  My husband feels it is a bit louder than he likes, but personally I didn't notice it. I felt it sounded more like soft white noise.  If you are sensitive to white noise, then perhaps this may be a consideration for you.