Stop n Go is brilliant - my last two tyres attracted a nail within 500 miles of fitting. I haven't had a puncture for 20 years for Pete's sake, then two, one after the other, on brand new tyres! The Stop n Go mushroom meant I got every last mile out of the tyres 1 managed about 14,000 the other was changed at 15,000, but it needed a new mushroom for the last 1000 miles as the first one had worn and was leaking slightly so the tyre went down in a day to about 12 psi. Rode home on nearly flat tyres more than once - too lazy to do anything about it, provided I kept the speed up the tyre stayed round!