I didn't wear one for years, after my Mum bought me a medallion when I was a kid, and I got teased at school...this was teh 80s though, and I don't think children are so unaware these days! I know have a stainless steel one, which just has my name and the word diabetic on it. I had a beautiful silver one, that I actually liked as a piece of jewellry, but it brought ne out in a rash, so I am on the stainless steel engraved one now.
I am in the unfortunatel position to have needed these on a couple of occasions, so I know from experience thatthe ambulance crews who were called to help me looked for id. Once they saw the word diabetic, it was a blood glucose check, and a glucose drip, and 5 minutes later I could give them all teh details tehy needed! On teh occasion whn I wasn't wearing any id, I went into a severe hypo outside my GPs surgery, so they knew me and were able to help.
The period of my life when this happened was when I was pregnant, and had never happened before or since. (when I say never happened, I mean to an extent where I could not communicate somehow). As Kegsrore mentioned, if teh only reason you wear one is to help put loved ones mind at rest, this is worth doing. There are so many out there. Personally, I don't think signig up to a complicated service is necessary..if you are hypo, they will treat that firsta, and sort teh rest out when you can tell them the rest.