Friedrich Air Purifier is great, for specific purposes.
My feelings about my Friedrich C-90A Air Purifier/Cleaner are somewhat mixed, but are mostly positive. I'll put the negative first, but it's a Biggie. It puts out Ozone, which is questionably dangerous for your health, and can definitely give me a headace. From everything I've read, it puts out more or less depending upon which particular unit you happened to buy. I bought one over five years ago, and have no idea why I didn't just return/exchange it. I point it at an angle to a wall and the fan helps break up some of the ozone, and that helps, but it's still there a bit, so I run an additional fan to help. All that said, there are some major positives that make it useful and worth keeping. Firstly, the filters can be rinsed in the shower or even put into the dishwasher. I also own a BlueAir, and the filters are insanely expensive, so I don't change them as often as I should, or run the BlueAir as much as I'd like to. Secondly, it is just fabulous with smells. I usually leave it in the kitchen, and turn it on high for fish and curries, etc.