I also got this Vertax D12. I can say it is really similar to the orig grip. the material is also polycarbonate like the real one. Functions also similar to the orig. The D800 can detect that it is D12 battery grip on the menu. I purchased mine on BnS section for150 sgd. Happy that I had bought it rather being rip off by the price of orig one.
Just some thoughts on the third party Pixel grip that I just bought. Haven't actually used the Nikon version, so this is really not a comparison per se.
Good feel and leatherette is nicely wrapped. Plastic quality if reasonable, paintwork/finishing is not the hard shiny plastic but looks to the D800 body itself (I'm referring to the finishing, not the mterial, which I think is only plastic).
Tried with 8xAA batteries as 3rd party EN-EL15 don't seem to be available in the market yet. After 400+ shots on 8 x 2700mah Powerex, the battery indicator on D800 still shows as full.
The shutter button on the 1st set I tried was quite fiddly, and makes a clicking sound when I half press the shutter button. Asked the shop keeper to let me try another set. 2nd set was okay.
Didn't like the catch mechanism on the battery tray as it doesn't seem very sturdy. I supposed it will last if u take precaution not to overturn or use too much force.