With cheaper or less well known companies, you usually don't get all the fancy driver stuff like Diamond or S3 provide (like the special Desktop Properties tabs which let you adjust various settings or tweak things; if they use the straight nVidia drivers, you're unlikely to get anything like that). You also run the risk of getting bad support, since they're not a big name company. Plus the product could just suck. Just because it uses the same chipset as others doesn't mean it's the same card. They may buy the not-perfect chips from nVidia, which couldn't make the higher clock speeds, and therefore your board would both be a slower version and be non-overclockable. Or they could have designed the board badly, it is totally possible to make a board which is flaky despite being the same chipset as better boards, plus, a small company isn't as likely to have the 'best of the best' designers.
On the other hand, you also might get really good support, because being a less well known company, they can't depend on their name to make sales, so great support and word of mouth might be the only way to make a name for themselves. And if they're using straight reference drivers, you don't have to worry about weirdness if you download new ones from nVidia. And a small company is more likely to either go out of business, or stop providing support for a product line if it doesn't sell well.
Of course, someone always has to be the first to use stuff from the lesser known companies, so it might as well be you. Then come back and tell everyone what it was like, and maybe the company will start making huge sales.