I found out I was allergic to penicillin as a child. I have a strong reaction (hives, throat-closing, the whole shebang) when given that antibiotic. Unfortunately, as someone with a faulty immune system, I get sick easily and get prescribed antibiotics often. It is imperative that my doctors and nurses know that they not give me penicillin. It isn't always possible to talk, depending on my breathing and other aspects of my condition, so wearing one of these is seriously something I find necessary.
They come in a set of three. I find them to be smooth and easy to wear. I like the idea of kids wearing one to camp, on sleepovers, etc. Plenty of parents worry that their children will accidentally omit their allergies. I also think they would be great to throw in your just-in-case hospital bag to slip on in the car ride over during an emergency.
I really think these are a must-have for those with that allergy. It can make a real difference.