The only difference is the quality, I know the Hamel ones are a bit hit & miss with their quality. I personally went for the genuine BG-E3 for around £90 then added a couple of batteries. c4rm bought it off me and it's still going strong
I don't mind buying cheapie bits for some things but when it comes to the camera I go for genuine so I have some warranty and assurance of quality. Now before you all harp about inflated RRP's and not all genuine stuff is good, my experience of genuine stuff is good and I have the cash to spare