Hi,
I own a DJI Phantom 2 with a H2-2D mount and I am looking to upgrade my setup to the GoPro Hero 4 Black with the appropiate mount.
My question is, are there any benefits in buying the H4-3D mount over the H3-3D?
I have searched and watched a few videos and i cannot find anything on the difference between the two mounts other than the size.

I know that the H3 can me easily modified to work with the Hero4 and I can find them used for cheap.  

H3-3D and H4-3D mount can exchange

H3-3D and H4-3D mount can exchange

Gimbals are balanced to a specific camera, though there is the possibility to modify the h3-3d, the h4-3d was designed for the Hero 4.

Because it was designed for the Hero 4 it balances perfectly, by adding coins etc (though some people may be able to) you may not get it precise leading to damage to the gimbal.