The full gimbal package got my interest more. Trust me, I believe in "buy it one & buy it right" theory
The point of the side-mount gimbal isn't that it's cheaper. Like you, I had planned to get the full gimbal initially. I called and asked RRS, and they actually recommended the side over the full (meaning less revenue for them). According to them, there's no difference in support. The side mount allows me to reach under the lens to easily access the focus/preset rings, buttons, etc., through the space that would otherwise be occupied by the bottom mount. The side mount is also fewer pieces, so it's lighter and less cumbersome for transport.
Personally, my RRS PG-02 LLR works perfectly with my 600/4 L IS II, with bodies from the 1D X to the EOS M, with TCs, a 600EX-RT + Better Beamer, etc.
Also, with an L-bracket on the camera and a nodal slide, the PG-02 LLR becomes a multi row pano rig (as can the full gimbal, by replacing the cradle clamp with an FAS sliding clamp).
One final thing to consider, when using a gimbal having a leveling base on the tripod is extraordinarily helpful, and if you plan to convert to a pano rig, one is necessary.