Product review (5 stars): EFFECTIVE!
It works.  Stop getting pink stuff and slime after just put a bit in the humidifier.  I do still use RO water though, not sure if that makes a difference.  I prefer this particular brand because it requires smaller dose.  By the way, I use honeywell's germ-free humidifier (and it's not really germ-free unless you add this), just FYI.