I'm using GoPro 4 Silver with H3-3D. Working perfectly here and excellent balance. I think the screen on the rear acts to balance the gimbal. If I release the camera it doesn't droop forward or to the side.
I did have to disable the power wires to the USB connector to stop some noise in my Vision app (I'm using GoPro with Phantom 2 Vision+)
I could get my GP4S to partially work with a GCU/non phantom environment by adding adding weight(penny) to solve balance issue. Connecting the usb side cable to the Phantom didn't work so I power the GP4S with its own battery and do not use it for fpv display as I had hoped. Also hoped the H4-3D would solve the GP4S issue but it specifically says it only supports GP4 Black. Wish DJI would specifically define what can and can not be done with the GP4 Silver.