I actually own the Phottix Magnesium grip for the D800(e) and I think you will be happy. The big thing that all the aftermarket grips 'cheap' out on is the the tightness of the locking wheel - it locks the grip to the body rock solid (with no obvious gapping) but the wheel itself has some play and feels a little loose - the Nikon Grips' wheel is always rock solid and tight with zero play.
Other than a little rattle here and there from that wheel though, the rest of the grip is solid, looks and feels like the real thing and works perfectly. A normal L-Bracket made to fit the D800 + MB-D12 fits (which is not always the case with aftermarket grips).
When I bought mine it was easily half the price of the Nikon one and I was only getting the grip for the advantage in handling/ergonomics - so I was prepared to save some money on this.
Phottix tends to make pretty decent quality products and this is definitely one of them.