I love that fresh-after-rain-storm smell ...

I purchased two of these units in 2003, when they were branded Neo-Tec, hoping to resolve an issue I had with pet dander (more specifically, fine, cockatoo feather dust.)  It did not work and I would say it failed on that front.  It did nothing for the dust except make it (the dust) stick to everything: walls, appliances, expensive drapes!  Had I done my research, I would have discovered then that I was trying to use these filters incorrectly. 

After putting them away briefly, I pulled them out to try again.  This time, I placed them in the bedrooms.  Our bedroom has body odor and dog odor.  It's always been strong -- someone just has a lot of sweat glands and it is not me -- and our dog, she sleeps on the floor, just adds to that.  Within a day after placing this unit in our bedroom and turning it on HIGH the odors disappeared and it smells like a rain storm in our bedroom!  This is amazing.  After the first day, I have only had the unit on low and it is working wonderfully on the low setting. 

As for sound, they make close to no sound except for a faint hissing noise.  It is very faint.  When the hissing noise grows a bit stronger/louder, it is time to clean off the plates.  The cleaning process takes about 10 minutes and I do it once in a very long while, perhaps 6 months.  It involves removing 2 large screws that, once loosened, can be undone by hand.  This allows you to pull out a set of plates (in one piece).  I rinse them and wipe them dry then go over them with some Q-tips to get into the crevices. 

I have read that there is some danger of these units creating a lot of toxic ozone when they are used.  My understanding is that ozone smells like bleach and is nauseating.  Negative ions, what my units seem to be producing, smell like "rain".  The air actually "smells" clean and crisp to me when I have the unit on.

I highly recommend these units to address odor issues, specifically.  For particulate filtration (dust, dander), use a mechanical/HEPA filter.

I've had these units going on 5 years now and they are working as good as new.