The two Pixel grips for the 5D MK lll I've used have good fit and finish and seem fine, especially for the price.
The shutter and AF buttons work well.
The problem is the electronics. When the grips are turned on, the multi- controller on the camera body doesn't work properly. Turn off the Pixel grip and normal function returns to the body.
It's too bad because the price is great. I don't know if the problem has ever been corrected. I've heard of battery drain problems but haven't experienced that.
I'm saving for the Canon grip. I won't return the Pixel grips because the high cost of return shipping and it's not clear the company would return my money.
It's the last time I buy outside of the USA and Canada.