Mine just arrived today. As far as I can tell it's completely functional. The batteries fit fine, the mounting to the camera seems fine, all the buttons work, it recognizes the shutter count and remaining life on each battery (one of which is the OEM, the other being a SterlingTek), etc. The only negative thing I can say about it is that the shutter button feels different than the one on the body. Works great. Just has a slightly different feel. I'd assume on the OEM version the feeling is nearly identical. I guess one other thing is that the plastic wheel that you use to turn the screw does seem like it could be a little more robust, but it certainly does not feel like it's going to fail or crack at any moment. That's a pretty critical observation, and I don't think you should avoid this product because of that. Just trying to be thorough.
The ergonomics seem to be just fine, but I've only been taking throw-away shots around the house. Haven't done a full day shooting with it yet.
One thing I wonder about is that the instructions are very specific to mount the grip to the body first and then insert the batteries. It says that if the batteries are in the grip first that the camera may not recognize them. Made me wonder if the OEM grip comes with the same advice, but so far I've been too lazy to check.
Obviously time will tell if it holds up or not. I bought it from a seller on Amazon named "dslrkit" who no longer has it in stock, and it was cheaper than buying it on eBay. It shipped from China. I've only had it for about two hours but so far I have no regrets.