Product review (4 stars): Filters last so much longer, cleaner air.
This serves a very basic, yet extremely important, purpose.  It keeps the water and filter in your humidifier clean.  I was reading that a huge number of people are doing more harm than good with humidifiers because they aren't keeping them clean.  They tend to filter out your air when it passes through the wick and that bacteria just collects in the filter and in the water.

This solution does a great job at reducing that bacteria growth.  You still need to rinse the filter and clean the basin of your humidifier often, you just have to do it less and you don't need to replace the filter as often.  This works best than anything I have been able to find at Lowe's.  And let's face it, those protec cartridges are a total rip off.

This bottle of solution has lasted me for at least 4-5 years and I still have plenty left.  It doesn't take much and you do not need to add it at every filling.  I usually add it to the water at every 2-3 fillings, otherwise you will see more buildup in the water.  It has no smell like adding bleach does (I've read some people do this, not a great idea!) and it keeps the filter substantially cleaner.  No more science experiment in your humidifier.

I highly recommend rinsing the filter out at least once a week, it will run much better.  You will need to switch out your filter reasonably frequently or it will cause buildup.  If it's one of the metal filters... running hot water through it may prolong the life.  Paper filters just need to be replaced.