It's not for all dementia sufferers I hope as that would be invasive and "1984" - not all sufferers by any means go wandering. My mater for example is one - awful memory on what happened an hour ago. I took her shopping yesterday afternoon and then on to tea with two of her friends. We came out one and a half hours later and she had already forgotten that she had been to Sainsbury's and then to my sisters she moans that she hasn't been out for days - if she can remember their names - her grandchildren she has all forgotten.
However, a wanderer she is not - God help it if she was as this is seriously rural around here. One of my closest Uni friends (my 2nd family as I call them), well the Dad was the antithesis of my mater, could remember family names to up within two weeks of his death but a real wanderer, almost as bad as my mate's labrador. Top have a tag on him would make a lot of sense to cost and family worry.
However, there needs to be a clearly defined process of when and how these tags are fitted. They probably won't be in a mental state to make the decision on wearing such a tag, so in my view it is he/she with lasting PoA (power of attorney) and the local court who should play off with each other, perhaps working with the local dementia unit/specialist as the neutral for evidence in all of this.