I actually ordered one of those. They made me a little nervous, there isn't a safety release. They are made out of climbing rope and have 2 metal things holding it together. The rope will slide between the metal to get bigger or smaller so in theory it should be able to be made bigger if caught on something. But it took quite a bit of force from me to get it to move, so I was a little nervous about leaving it on the cats.
Most vets/shelters around here have the scanners, but not all chips read on all scanners. I have both dogs chipped, but don't have the cat's chipped.