The locking mechanism breaks the plastic teeth that are supposed to hold the extending arm in place under the skate. I bought the junior pair for my son and the teeth broke after just a couple of uses. Thinking I could be more careful I bought the senior weights for my older son and myself with the same results after a couple of uses. Also the lock is hard to close if not in the exact spot it needs to be which adds to the frustration of putting them on when you have your skates on. I did get to skate with the weights awhile and it made me work harder and I could tell a difference after skating a couple hours. I think it will help performance but for price and design flaw, not worth it. A good stiff spring instead of the locking mechanism could benefit this product.