Summary: I had the extra battery grip for my D200 and on upgrading to the D800 it was on my list of must have accessories. The grip gives you the added battery power/longevity and also the increased frame rate. Not withstanding this, having control buttons on the grip as well allow easy operation at any angle. I find that the standard camera is slightly too small for my hands and the added depth with the grip fitted allows me to confidently hold single handed.
Pros: Durable, Great Features, Great For Larger Hands, Grip
Summary: So, I've used the MB-D12 on my D800 and I'm very happy with its performance so far. I've got that extra FPS boost I need for action shots. I didn't want to pay full price, but didn't feel comfortable with a 3rd-party grip...getting it on sale was the best choice for me.
Summary: Very well built grip, D800 is my 1st non pro size body and did struggle with it in the hand for a few weeks so decided to get the grip, the connection is very firm and feels good in the hand and makes the camera feel more secure in the hand