Lots of things are effective. Steroids are effective. Ritalin is effective. Stealing signs is effective. Caffeine is effective.
as with all things, you have to weight the risk/benefit ratio and perhaps most importantly factor in individual genetics when making a decision.
if I was going to have my Kid do a weighted ball program, there are two things I would absolutely do:
1). Have my Kid evaluated by a very highly rated strength & conditioning expert looking for muscle imbalances and weaknesses, and then train to correct those weaknesses and imbalances before beginning the program
2) I would have my Kid do the weighted ball training in person at Driveline's facility.