Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Best air purifier

I have purchased many air purifiers in the past, but this is the best one so far. I have 2 of these. They have been running continuously for a few years. The outer charcoal filter is easy to remove, and I have been vacuuming away all the dust and cat hair that collects on it. What sold me the most, is the permanent HEPA filter, which you just vacuum once in a while. The company is great to work with. They answer the phone right away, and will send you a brand new machine if you are having problems with it, if you send it back along with a ten dollar check.PS, I am a physician who has asthma and 3 long haired cats, and I think this machine is worth having in the home. I have one in my living room and one in by bedroom. It has 3 speeds, and is fairly quiet compared to other brands. It is lightweight, portable, and easy to care for.