I am pretty sure they are only meant to be used in an incubator due to their design, not sure that they would work well if used as a stand alone container left on a shelf.
saw these containers for sale at a show over the Summer and they had a video presentation of it. They seem to work really well, i picked up a few, but i have no eggs so far so need for me to use them yet. not planning on breeding anything til Spring.
http://www.multiscope.com/hotspot/herplyon/rbrood1.htm
that is one of the best if you are willing to spend the money, keeps the temp within half of a degree of what it reads.
not a good thing to use, you are better off using a watering system with a sponge. I have heard nightmare stories of animals that were fed crickets with that ate the crystal and then later expanded to their deaths as the crystals hydrate inside the animals.