The genuine Nikon ones are selling on eBay for £100+!!! Thanks for bringing that to my attention, I forgot I own one of these (I know, how do you forget right!). I'll have one on here as soon as I get my post count up to 100.
For the relatively small difference in price I would go with the genuine Nikon one every time, when I looked at these (about a year ago), the build quality was far superior than any of the copies I looked at. Just my opinion, but there you have it.