The "gizmo" is commonly used with facial rigs. "Gizmo", simply referring to any control with multiple functions mapped to it. Here I use it in a less traditional role.
The shark rig in the video was a precursor to the final rig and helped determine what could or couldn't be procedurally animated.
Keeping up-stream and down-stream control handles from diverging in overlapping controls can be tricky. Much like compositing, when the jobs done right, you can't tell there was anything at all.