My son has trained on all machines, and they all have their benefits. But using anything exclusively is a bad idea. We knew they used a 2 wheel Jugs machine at the High School level and for the tryout. So he practiced hitting off one during the winter. But we would always compliment that practice with live arm throws as well as using a local Iron Mike, which is much more similar to timing live pitching. We used a ProBatter PX2 on the weekends to simulate live game at bats. You should do the same. Have your boy get in extra swings outside of practice from a live arm or the other machines I listed. Use the time on the coaches machine to work on a specific aspect of the swing, and don't treat those swings as live at bats.