I've had mine for over two years now.  I've never had a problem.  They're firmly affixed to my Ray Bans and keep them securely with me.  I have in the past relied on the cord type which work but not as well as these.  I find I like this wire version better because it doesn't get caught when I put on or take off a jacket.  I keep my sunglasses hanging from my rear view mirror, or from a hook next to my keys in the house and with cablz, my glasses are kept safe from scratches and ready for me to need them.  I highly recommend these if you want to take great care of your expensive sunglasses or any glasses for that matter.  I'm not one who loses things a lot but I know many of you are.  You lay them down on a table and forget to pick them up and take them with you.  I think this device will help you keep better track of your glasses and keep them securely with you hanging from your neck.