I was buying a Ford car a few years ago and the salesman tried to talk me into buying GAP, he convinced me it was a good idea, but the cost put me off. I did some research on line and took out my own policy with car2cover.co.uk and found they were alot cheaper. Not having had to claim I cannot comment on how they are with dealing with claims.
I'm in the process of buying a new Audi Q2 and will be buying again, even though it might never be used it is just for piece of mind.