I had one I used on the Appalachian Trail,,our radios didn't work well in the mountains and the Forest Service decided that it was a necessity for me to carry one for rescue work during one particularly hot summer when we had tons of heat related rescues that year on the trails.
They do work quite well in those circumstances and I'm positive it saved many lives that year, we had over 200 heat related rescues and a few deaths that one summer alone sense it was consistently 85-90 degrees+ and most water supply's had dried up. It was a very tough year and took a toll in the backcountry. I don't know if they kept them in service for long or if it was just during that hot spell, I know the CLEO's had them longer and used them pretty regularly. I can't say for sure if they still do or not. I haven't worked with them sense 03. They were almost as big as our radios at that time, but one I saw just recently is about the size of a regular cell.
Definitely a cool tool.