I switched to three under based on Rick's recommendation when I attended his class for the first time, some years ago. I have shot three under ever since, and have no inclination to change back. Interestingly, a few months back, I forgot to put my bow in my car for my regular morning shoot with my friends. One of my friends had a spare Hill style longbow with him that he offered to let me use. Always nice to have friends who carry extra bows with them. His bow was set up for split, and my feeling is that Hill longbows are best shot split anyway, so I shot split fingers that morning for the first time in years. I didn't win any prizes, but I enjoyed the experience of shooting a type of bow I normally don't shoot in a style I normally don't use. By the end of the day, I was actually hitting things I was aiming at with it.
If people don't want to shoot three under, he is happy to teach them if they want to use split, as the string grip is not an essential part of his style.
What is an essential part of his style is the dead release. It would be a waste of time to attend Rick's class if you are committed to the dynamic release.