I recently purchased the Alen BreatheSmart 75i air purifier and the results have been amazing! I suffer from severe seasonal allergies and asthma and this has significantly improved the quality of my life and sleep. I hardly cough during the night so I sleep much more soundly and I have not had to use my rescue inhaler while in the area where I have the air purifier. 

The unit is also extremely quiet, but yet still seems to block/dull external noises, which also helps since I am an extremely light sleeper.

I highly recommend this unit! My only regret is that I didn't purchase one sooner!