I spent a lot of time looking at these, mainly reading reviews etc on Amazon, but was really unconvinced. The fact that the baby wears it and so must be supervised with it on was worrying for me and also that there is no evidence really that it makes any difference.
I bought something called Teething Bling, which is fabulous, its a necklace that mummy wears, which looks like a real necklace but its actually made of silicone suitable for babies. So when my little one grabs my jewellery and puts it in his mouth it is actually there specially for him. I got the turquoise necklace and braclet. The bracelet looks rubbish, I dont recommend it as fashion wear, but it is useful to have a toy for him permanently on my wrist that i can pull of and hand him to chew when necessary. But the necklace is genuinely pretty and i might invest in some other colours. They have loads, they are about £12 or £5 for the bracelet. i went directly to the website because they take paypal and had more choice but again you can get it on amazon.