Abt 18/24 months ago when my son was becoming more serious about his pitching role, I bought a 4oz and 6oz ball. I looked into what was out there for pitching programs, and I settled on the Steven Ellis format that has been around forever.
Warm up with regular 5 oz baseball
3 minutes at 70 feet
3 minutes at 90 feet
3 minutes at 120 feet
1 minute at 70 feet
Then, at 70 feet, I would do:
20 throws with the 6 oz overweight ball
20 throws with the 4 oz underweight ball
20 throws with the regular 5 oz ball
Cool down
I am a big fan of the KISS principle. If you make something too complicated then the kids won't do it. The overweight and underweight ball is only 1oz difference. I suspect injury would not come from the weight difference, but from not doing it safely - failing to get the arm hot, overthrowing, etc.
Anyway, my son refused to do it. He is not willing to risk injury for improved velocity. So the weighted balls are collecting dust.
And that's what I have to say abt that.