I am only an average player, and not very particular about tennis balls. However as soon as we started playing with these balls, we noticed that they were different from what we were used to. These balls feel very hard - almost like hitting a stone. They bounce OK, but when hitting the racket they feel heavy, without life, and send vibrations through the racket. I had plenty of other balls with me today and switched back forth between them. the difference was immediately noticeable. I will keep these balls for training the kids, but will not use them for regular play.