they hold up really well, like Scotty said, they come with credits, and when you buy a used one some of the credits are used, so you might save 100 bucks initially but if it doesn't have any credits, they it's not doing you any good. they rarely sell for less than 300 and when they do, they usually have no credits, so you are really only saving 100 dollars, and if you tune 2 cars then it's not saving you anything.