With respect to those above - and acknowledging that I seemed quite outnumbered on this view - I do find the cheap simple ones to work wonders for me. My allergies used to be dreadful, but I have no problem at all now with a simple unit that is basically just a fan to pull air through a replaceable HEPA filter. I have never tried the rabbitair - I have no reason to doubt it's quality - but at least for me the far cheaper solution worked quite well.