Amber teething necklace?

I'm not nor will I ever use one. I just don't think putting anything around my baby's neck like that is safe. Just wondering what your views are on them? A friend of mine is getting one and laughs at all the warnings out there that they are unsafe. Has anyone had a bad experience with them? I have read about some babies almost being strangled by them and having them get wrapped tightly around arms to the point of cutting off circulation. This is by no means meant to be negative to those who use them, I'm just genuinely curious.