3rd party battery grips?

I own a nikon D90 and was thinking of getting a battery grip. But I wasn't sure if I should get 3rd party ones. I don't want to spend so much money on a genuine one but yet again, how bad are the 3rd party ones? My dad says don't get 3rd party ones because it will send an uneven amount of volts to the camera and it will fluctuate.eventually the camera will stop working.
so should I get a 3rd party one like this?

http://www.ebay.ca/...0607953683

Putting an aftermarket grip on your camera would be an insult to your camera. Many 3rd party grips have cheap/faulty wiring that could fry your camera.

How bad? There's a reason it is cheap. Are you willing to find that out while using it with your camera?