It's off an Orbea, it's off a year-old Onix, which was a 2600+ Racing bike. Unless there is something structurally or aesthetically wrong with the fork by use, the fork should be great. Having ridden an Orbea, I can say I wasn't scared to break it, but I'm talking about a bike from 2004 (it's still ridden professionally [not by me, obviously]).
For 50 bucks, that's a stellar deal in my book. Just make sure it's in good shape, and that the steer-tube is long enough for you!