I took a polishing class at CG. Not their full detailing university program, just a one day Saturday thing since I am an enthusiast, not a pro. It was helpful to have Greg monitor my polishing with a DA, and I learned to use a rotary enough that I feel comfortable using one even though I dont need to with my car. It was also helpful to be able to use and compare flex 3401 vs PC and the results you can get from those machines. Bottom line is that I was able to refine my techniques with coaching.
There are much more in depth courses out there such as the ones you mentioned and the one tought by Renny Doyle at detailing dot com in Southern Cal, that are oriented to pros looking to enhance their skills and develop a business. I would do it if I was going to do this as a business. There is a lot more to it than just polishing paint if you are doing this to make money.