Not backup quality?
There seems to be a developing trend for manufacturers to sell their latest drives in consumer USB disk packages before shipping them as internal drives. Might this be a sort of post-beta testing, on people who are much less likely to sue if the bleeding-edge tech proves less than perfectly reliable?
Anyway, my warning is that "random" USB drives are not a good choice for backing up important data. Build your own using a marketed internal SATA drive with a 3 or 5 year warranty and a USB enclosure. Better still don't risk your data through a cheap "random" SATA to USB chip. Use E-SATA, or a SATA drive in a swappable caddy.