None at all. Having owned the UPO (quite a few haha) I didn't think I would be that impressed by the gen because the UPO is built really well. However, it really did exceed my expectations, the fit and finish is really very good, Im really pleased with it.
When you get the UPO see how you like it. Personally I couldn't live with the little flaws, I think it is perhaps because I adore the genuine so much, so it never quite met that level. However, if you don't mind the little flaws there really is no reason to get the genuine. The UPO keeps great time (usually) and it is built very well. With a double AR coating, on the wrist it looks almost everybit as good as the genuine. I was certainly shocked at howmuch better the UPO looks with an AR coating when I got Bwhitesox's Orange PO. The double AR completely transforms the replica from a good rep, to a great rep!