The side grip on the Movi arm is more versatile and fast, mainly if you have AF and want locked in some situation.
The problem with relocating the side grip is it is an extra cable that could get in the way of the movement. You can also remap the auto focus control lock to the body. Check out the video on this blog http://outsideinstudio.com/blog/fun-with-the-movi-m5/
I bought a Startech Trrs jack extender for a grip side Canon C100. The cable has a 4 conductor like B&H advise but not all the function are available. Only the joystick and REC button play, while the roller for diaf and button 7 are not available. sheet!!!! I would thange the ISO on fly and could block AF in some moment... I wonder if what f...k jack Canon is implemented!!