My long-time teacher, Larry Skinner, studied under Gordon for years.

He would agree that SA by Gordon is not realistic for amatuers, and maybe not realistic for most pros. He would also agree that Gordon's lessons provided a lot of information missing in the book, and that CG's approach in person was very different from what most read in the book. Finally, Larry would have agreed with the poster who said they don't like Gordon's approach to trumpet -- certainly not his written approach, though his lessons were valuable.

Larry dropped about 1/2 the Gordon approach and mixed it with about 1/2 the older Callet Yoga approach, and did so using some Reinhardt methods: study the player, and make adjustments as necessary to the overall approach. When he taught me, he focused more on the Callet side mixed with a lot of Clarke stuff.