Their service seems to be a bit 'hit or miss'. i.e. some people get what they pay for (and subsequently provide very positive reviews) but others don't (and then provide scathing reviews).
See here:
http://www.resellerratings.com/store/product_key_downloader
The US-based Better Business Bureau has some positive reviews listed but there are also these complaints:
https://www.bbb.org/south-east-florida/business-reviews/computers-hardware-software-and-services/product-key-downloader-in-pompano-beach-fl-90308036/reviews-and-complaints?section=complaints
Companies which sell cheap product keys often get them through harvesting the data stored on redundant computers. (i.e. they're
used keys; given that Microsoft no longer sells legitimate keys, that's not surprising). If those computers were never used online (as many office computers aren't), or if the Windows 7 installation was never registered with Microsoft, there's a good chance that such a used key will work on another computer; however any key which has already been used to connect to Microsoft's servers won't work elsewhere.