Product review (5 stars): Simple and Useful
For those that can't figure out what this is even after reading the manual:
This is a fabric pad that goes on top of your ceramic or stainless steel heating element in order to absorb the minerals that usually accumulate on your heating element.

The way to use it is pretty simple -- plop it on top of your heating element, then use the humidifier as normal.

However, during my tests, I've found that I really can't "go longer" with my hard water -- if I do that, the fabric pad would end up "bonding" with my heating element due to all the extra minerals accumulated in between them, and I'd end up with a mess.

If I stick to my original cleaning schedule, then, when I take the pad out, the heating element only has a really thin layer of minerals instead of the half inch thick layer of cruft that usually accumulates.  Because of that, it saves me time in cleaning my warm mist humidifiers, so that they can be "returned to service" much quicker than my old 2-3 day cleaning time.

And, the pad itself is pretty easy to clean too -- put it in 3% vinegar for an hour, then squeeze dry, and it's ready for use again.