Tom House and Molan Ryan are co authers of several books.
I understand but there is no need to spend huge amounts of money. We used books to get started and had various coaches tweak TJ's mechanics. We had different opinions from top level coaches and listened to all of them. He did what was comfortable for him. A college player who helped coach his varsity team tried to totally change his mechanics. He asked me what to do and I told him to try his method. He tried it but reverted back to his original motion during the games. The college guy was trying to help but TJ was not comfortable with the motion.
House's method may not be right for your guy but it won't hurt him either. The pitching motion is not a natural motion and you have to find what works for you. It may take time to adjust. I know lots of guys who went to a very qualified pitching coach and said they pitched worse than before they started.