I bought one of these "MB-D51" grips
BRAND MB-D51 Battery Grip for Nikon DSLR D3100 D5100 NEW IN BOX | eBay
on eBay from a seller called "sex-point168." I won the auction for $55ish. It arrived yesterday.
1) This grip did not come with a Nikon EN-EL14 battery as the listing said it would. The auction said:
"The Battery Grip comes with one EN-EL14 Lithium Battery, one Infrared remote control and one D3100 Connector Cord."
2) It is not the grip pictured in the auction. The grip in the auction has a rubber grip. The grip sent does not.
3) The instructions in the box do not match the grip and were obviously written for a different grip as even the product diagram doesn't match the grip sent to me. This is obvious regarding the storage of the D5100's battery door. The instructions show a place for the door that does not exist on the grip you sent me (item #10 in the instructions).
4) There is no place to put the D5100's battery door in the grip sent.
5) It's obvious this is a counterfeit grip since there are no serial numbers on the grip or box and Nikon doesn't make an MB-D51. The Nikon sticker on the grip doesn't quite fit the indentation made for the sticker. It's very cheapy and the included cable obviously wasn't made specifically for this purpose as it is too long and requires an awkward bending to fit.
6) There were no form-fitted cardboard inserts as Nikon always has for their products. There were only bubble wrapped and bagged items including a NON-Nikon remote control. FYI, an ML-L3 works with the grip I was sent. I basically received this:
Pro Battery Grip for Nikon D5100 EN-EL14 ENEL14 DSLR Camera+IR Remote | eBay
in a nice genuine-LOOKING Nikon box that is not genuine.
It's CLEARLY counterfeit. NO question about it. Nikonusa.com returns no search results for "MB-D51" and accessories for the D5100 does not list any kind of battery grip.
If you want the remote control (that will instantly fire the camera in whatever advance mode you are in as if you had pressed the primary shutter release button) ability, this non-rubber covered grip is the one for you. If you want the rubbery grip, you won't have the "anytime" remote control ability. The trade-off is up to you. Just know that Nikon does not make a grip for the D5100. ALL are aftermarket and mine, with the Nikon labeling and box, is straight-up counterfeit at a substantially higher price.
Seller has not yet responded to the email I sent to her yesterday. If seller doesn't refund me fully, this'll wind up being yet ANOTHER eBay fraud/counterfeit claim... Geez, I don't know why I ever bother with eBay anymore...