Most (if not all - I didnt get a chance to check out all the claims) of these are for POWERED by ATI cards,
which use ATI chips but are manufactured by other companies,
where as the ATI card on sale on ebay is an original BUILT by ATI card, which are normally alot more expensive than the POWERED by ATI cards.
So I would say its down to you if you buy it or not,
But I got the original ATI card as it is more likely to be supported by OS4, rather than the huge number of POWERED by ATI cards, which Forefront Tech may not be able to test on.
regards
Mostafa