Basically you buy a card, and if within 90 days of purchase you want a better card you can do it, you have to send your card back in perfect condition with everything it came with (you have to have bought it from a dealer on their list) and then you pay the difference in cost between the new card and what you originally paid for the old.
The reason I have an EVGA card is because it outbenched the BFG version in most tests I saw done, and since I was already spending a lot of money on it I wanted every bit of performance I could get without OCing myself. And it had the word "superclocked" on it
The EVGA and BFG were both substantially faster than a 'stock' version from someone else.