Product review (5 stars): Shocked at how much it filtered!
The water in my area is especially chlorinated, so I only use filtered water in my humidifier.  These still filter out a ton of crap!  My last one was so full & disgusting that it was frightening!  All of it was trapped in the filter, none of it made its way into the humidifier itself, so I'd say these are great!
I will definitely need to remember to change these on a regular schedule, right along with my shower head filters.  I wish they were available via Subscribe & Save.