Product review (5 stars): Pays for itself
I have used a cool-mist Holmes humidifier for many years.  Typically, the filters must be changed bi-weekly, and there is a damp smell at times in the room.  I bought a bottle of this recently, and it has totally eliminated the damp smell.  I've only been using it for a month, but it seems like the filter is lasting longer without having to change it.
It's a little bit of trouble to add it to the tank, but well worth it.  Filters are very expensive, and I think the BestAir treatment will easily pay for itself in just filter savings.
It makes the room smell fresh, sort of an antiseptic odor...very clean smell.  I just bought 6 more bottles so I'll have it around for a very long time.