I recently bought Windows 7 from these guys to install in bootcamp. The copies of Windows they sell are OEM versions (see this article
http://www.zdnet.com/blog/bott/what-microsoft-wont-tell-you-about-windows-7-licensing/1514?pg=2). However, I don't know whether they are System builder OEM versions or the ones that are only supposed to be used by major PC manufacturers.
The software installed perfectly and was already activated with Microsoft when it had finished installing (that is I didn't have to manually enter a serial number at any stage). I later checked the software with Microsoft's validation tool and it came up as genuine.
I was charged the correct amount on my credit card, so don't feel as though I was scammed.
However, there are many dodgy things about this company, which I wasn't aware of until after I ordered the software. Firstly, as has been noted, although the website claims to be based in the US, the company doesn't seem to be American. The transaction has appeared on my credit card statement as coming from Latvia. The emails I received immediately after paying for the software were in very poor English. The serial number that appeared next to my download information bore no resemblance to the OEM serial number (Product ID) in the installed system.
It's possible that the product ID is being mass-used in breach of MS licensing agreements and if so, I guess at some point my copy of Windows may fail the validation test, but for the moment I'll assume it's OK.