This is our 2nd unit - we bought our first from Amazon. We liked it so much we bought a 2nd. It's impossible to prove but our allergies have been greatly reduced since using it. Within a few days, we noticed that we're not blowing our noses and sneezing quite so often. However - all allergy related benefits are greatly reduced/lost once you go outside or open the window.
Every-so-often it lets out a puff/stream of mist. We put the first by the a/c returns for the best circulation in the area that treated the largest area of our home. Even then we saw benefits. The 2nd we bought directly from BetterAir is for the bedrooms.
Our 14 year old cat appears to be feeling better as well - she's more alert and playful. Our daughter visits weekly with her 13 year old Yorkie who suffers for a few years now from Valley Fever. He is improving as well - gaining all his pre-Valley Fever weight and is more active. Again - we can't prove any of these claims.
I have not seen a reduction in dust. I was hoping that it would magically disappear (joke), so ... I dusted. That was just yesterday and soon it will be "window opening season" and I suspect we'll be back to sneezing and blowing our noses. But - at least I got a break from my allergy medication and still have kleenex!