Product review (5 stars): Great
I've tried other means of controlling bacterial growth in my Honeywell QuietCare humidifier, but they have lacked.  Bleach is dangerous and has a scent.  Protec cartridges (the ones with silver in them) do not work sufficiently.

On the other hand, this BestAir stuff works very well, much better than alternatives I have tried.  It has very little scent.  Moreover, it is potent and so this bottle will easily last this winter, next, and perhaps after that.  Furthermore, I think some of the product remains in the filter, and so I only add the recommended amount to every other tank, and the results have been good. As a by-product of its effectiveness, my filter is (so far) lasting longer than before---but that performance might depend on your water-hardness, so mileage varies.