Guess what? Tennis doesn’t work that way. Tennis is such a complex sport, that the level of a player is mostly determined by the ability to bring together the various parts of his/her game. This integration happens at a neurological level, the speed in which you process information and the capacity to act upon this information. For sure you can “buy” parts, like a better second serve, better foot work, etc, however they only make a small percentage of the overall performance. The biggest improvement a player can achieve, comes from improving the capacity to read the game and take appropriate decisions. So if a player still does not posses this higher level, external tools should not be expected to create any kind of radical change in their game.