I've used it, DD has used it. It's the only device of its sort that is actually allowed by name in ASA play, so long as it is kept in the pitchers pocket. It cannot be set on the field like a rosin bag, and cannot hang out of the pitchers pants/pocket.
Bill Hillhouse endorses its use, I believe. It works very well in the rain or when you have a wet field/wet ball. Just don't pick your nose after using it, it might get stuck.