Purchased a space black link bracelet from them last year, I'm fairly certain it's genuine. Compared with one at the Apple Store and it was identical. Folded the same way, which was a big deal for me. I have fairly small wrists, and all the knock-off link bands don't fold the same way Apples does, resulting in more of a squeeze than contouring correctly.
It had some minor visual defects on the inside, which I think supports the idea that these are factory rejects, returns, or something along those lines. Totally worth it for a fraction of the price. Looking at getting a silver link band from them, having switched from space black for series 4.