My Meike grip for D750 arrives tomorrow. $62. I have a Pixel grip on my D600 that's worked flawlessly for 2 years. The Nikon grip I had on a D100 was great; the Nikon grip on my D7000 is not so great (sent back to Nikon under warranty for repair of rubber coming loose, problem came back a year later). That pushed me over to aftermarket.
I use grips to balance big, heavy lenses and for portrait mode shooting. And, on some bodies, it increase the fps rate.