They are probably knock offs. Considering the WD drive I used (250gb) cost $55 OEM, I would be wary of these. Reminds me of the micro SD cards that were 64gb being sold, but were really 16gb...
MS has the ability to ban you for using a knock off drive (even one flashed with original firmware like mine), but I highly doubt they will. Also, from what I've heard (and this has worked for my Xbox with the DVD drive flashed and my friends) if you just don't come online during the times when they ban (the big firmware updates), you will be okay. Of course YMMV and I'm sure someone will come in saying they were banned before or after and for all kinds of reasons.