Installed both FIT50 and FLEX same day. My wife has had severe headaches that Doctors were unable to pinpoint the reason for with their tests and scans. I installed these on the possibility that it might be air quality. Has only has one headache since, and that was when I had the FIT50 shut down for prefilter cleaning. It was not as severe as they normally have been. Also, my sinus problems are much better. Time will tell, but so far we are well impressed with the results.