They've been around a while - apparently they continally record the animal's temperature, which shows up on the reader along with the chip number when it's scanned.
Yup, my dogs got one. I think they are great, particularly if the dog is nervous. To be honest i would rather be scanned to take my temperature than have something shoved up my backside at intervals. We've just started offering them at work and most people are opting for them now. Particularly useful in cats!!