GF Performance chips?

A friend and I have been debating on how wonderful these performance chips really are. I can't really see how they can really do so much to improve performance while saving fuel yet he thinks they are the real deal (even though he won't buy one himself first). GFchips.com is the main site is the one in question. Any info/advice/real experience would be appreciated and if there are actually any sites that do have a type of worthwhile chip.