I actually have had a few of Doc Reinhardt's students study with me and take and graduate my trumpet upper register course with success!
I went through most of Donald's pedagogy and method...at least as much as I could find in writing and in his books. For me, it was complicated and not easy. Perhaps, for me, the timing was not right: I had already mastered a great deal of the upper register and extreme upper register when I gave Donald's teachings a try. Therefore, I can say I wasn't the most motivated to keep at it and really learn it.
That said, my course does contain one technique from Doc Reinhardt and I have actually tweaked it a bit for my program.