I bought some 10 wrap coils from Killerink in Liverpool about 3 months ago and they have been fine. I dont know how long they should last but I use mine for a few hours most days. I buy 90% of all my kit from them as their prices are good and they deliver next day. The only problem I ever had was my power pack that came with the kit I bought didn't work very well after approx 2 months, but they exchanged it for a new one no problem. The guy I usually speak to is Matt who is very helpfull even to us "Scratchers", they don't have a problem if your not registered unlike some other suppliers.