I have two. One came with a 5d mkII, the other was purchased from Amazon when I couldn't find the original (house move disarray) and the packaging of that appeared genuine.
Front looks identical (as far as I can see).
The labelling on the rear varies (i.e. all 3 are marginally different). The CE mark looks OK/genuine (historically I have compared CE marks on electrical items imported from China, and have found some which don't quite come up to the official dimensions) but I'd have to have it in the hand to be thoroughly sure.