My mom wanted to get one for me.  But being the good son that I am, I did a lot of research on it before letting her lay down the $400 for it or however much it costs.  Basically from what i found out, its HORRIBLE at cleaning the air, and even worse, then tend to break down very easily, and after about a month or two they are far from quiet.  It costs them like $30 to manufacture one, and they sell them for over 10x the price.  There are a lot of other problems too.  Just avoid them at all costs.