The only drawback is that, if it's anything like their computers, you don't get the super-pretty original box--you get a less exciting brown cardboard box (if they still do what they used to do with Macs) or perhaps a slightly prettier white box that looks only slightly less exiting than the original (as happened with my iPod a couple years ago). 🙂
Seriously, they're inspected (perhaps even more than originals) and come with the exact same warranty, so I wouldn't hesitate to purchase one at all. The discount is, of course, an added bonus.