Several 4.0 and above players use the TopspinPro. The reason is two-fold:

1. 4.0 and above players have usually mastered topspin but some may achieve it in the wrong way. If they wrap their racket face over the ball (following the curve of the ball) they’ll generate topspin alright but with inconsistent results as the racket face angle is constantly changing – hit it early and it’s out the back, hit it late and it’s in the net – there is only one point on the arc when it goes in and you need to preciseness of Jimmy Conners to do that! So the TopspinPro will help them change to brushing past the ball at the tangent. Much more reliable results. Much less effort and you swing the rack up in one direction so your arm can stay loose (unlike the curved swing of the first option).

1. Still-ball training. If you want to work on changing a part of your stroke (preparation, unit turn, etc), adjusting your spacing, improving your footwork, you need a ball to hit to keep the experience realistic and give the shot context. You can use shadow swings but nothing beats contact with a real ball.