The way I see it that the two plane swing uses two plane angles , one similar to the address plane and a steeper plane at the top.

The one plane swing uses the address plane throughout the swing but at the top it is parallel to the first although higher

Both require you to drop the hands on the downswing to get back into the release position and plane.

As mentioned earlier they become apparent at the top of the backswing where the one plane angles the shaft at the end of the shoulder, the two plane angles the shaft roughly half way along the shoulder.

__________________
Best Regards
Brian

________________________________
Funny o'l game!