Your right, probably not everyone would recognize a bracelet like this:
But at least hopefully the people who can save your life (and stop you from being kicked off of a train) would. In contrast, they probably would not even have a chance to notice a necklace that is hidden under clothing. If your passed out, etc. someone at some point will probably at least take your pulse ;-)
Just my 2 cents - I wear a necklace also, but the recent Amtrak incident has helped me change my mind. I just signed up with
Medicalert