I have been looking for some weighted training balls at a reasonable price for a long time and I was happy to come across these. They are great! They have held up well so far to all of the hitting drills we have done with them. They have not shown any more damage than a scratch or two when they have inadvertently been either thrown or hit into a chain link fence. They are noticeably softer after an adult (18+) hits them but it has not affected their performance or usefulness.My use of them has been primarily for hitting drills with 8-12yr olds. I have noticed an improvement in their hitting as they are getting better at driving the ball. For me this means that their is less "ball hitting the bat" and more "bat hitting the ball". Bat drag is a problem with most of the younger players I am around and using these has really helped to illustrate what that is and why it limits their hitting. They can feel the difference when they hit the ball if they drag the bat because the ball tends to slow or stop the bat. When they hit correctly they can feel the bat pushing through the balls.I have also used them as a tool for helping to teach them how to throw better. This has been done with LOTS of caution to keep them from hurting their elbows and shoulders. We never throw fast/hard or more than 10-15' depending on the kid. I'm not using the balls to develop strength, I'm using them to help the kids "feel" their throwing technique. The weight of the balls helps them recognize the difference between bringing the ball up to their ears and reaching back with the ball at the beginning of the throw. It also helps them to feel the difference between throwing with their arms and using their hips and shoulder rotation. If you can get them to slow down enough to listen and "feel" their techniques then it really makes a difference.All in all after a few weeks I am using the balls more than I thought I would and they have proven to be more than durable enough to stand up to what I have used them for.