Product review (4 stars): Thumbs up!
I use this to suppliment a whole house humidifier when the RH is low.  Works fairly well and easy to fill.  Depending on how powerful your hvac is and how high you have your heat the reservior will need to be filled quite often.  I have to fill mine 5 times a day.  Overall worth it if you need to suppliment without breaking the bank and using more electricity.  I have 9 floor registers and replaced 2 in separate rooms.