If you have a good camera angle, #1 lets you see what is happening both for plane, and for startup (swivel or not). Specifically if the startup swivel is on plane or not (if being used).
When you say "on plane" am I right in thinking you mean the path of the hands or specifically the #1pp vis a vis the Hand Path you delineated previously from Top to Impact?
Do you prefer that analytically to the Shaft/ Sweet Spot Plane? Or do you consider them both?