I've recieved my Alware Senrigan GP-35 gimbal, and have it mounted to the Phantom.
I haven't flown it yet, but tests here on the ground look promising. I just had to assemble all the parts, and power it up, and it works as it should. I also got the tilt working with the 7th channel on the stock transmitter. When rolling or tilting the Phantom it seems to do a good job of keeping the camera steady.
The chassis holding the GoPro in place looks like aluminum, or a similar light metal material.
A minor drawback is that you need to loosen two screws to wiggle the GoPro out of the casing, but other than that it seems to be a good product.
The installation manual is mostly very good, but with a couple of confusing/unclear steps, but I emailed Alware and got most questions sorted out.