Varsity tennis player here. I have been using my fitbit bracelet for a couple months now, I have to admit that the device is inaccurate. I am pretty sure it undercounts running distance and number of steps. We are talking about big wide steps that happens in a consistent manner. A players movement on court is much more complicated. Such a bracket for tennis players needs to be much more accurate than my fitbit flexband to be useful. A good tennis player never takes a wide big step, almost all the movements on court are quick small steps. Unlike running, a player changes direction all the time. It would be really cool if the bracelet can give the player data about his footwork but I think the emphasis on this particular product is on the actual technique. Man its not easy. Sure there might some easy wins in the beginning, like counting how many forehands or backhand a player hits or things like how hard have you been hitting the ball. But I think its extremely hard to dig more into it. “How much spin are you giving”, “Are you hitting the ball late or early", “How fast can you recover when you hit the ball(combine it with footwork)”, “How high is the ball when you hit it” “Are you bending your wrist too much, or is you elbow really close to your body”. “Are you hitting the ball just with your arm or your shoulder and your waist follows through with the movement" These would be the questions that an intermediate tennis player would be interested in. However I am afraid these all happen in a fraction of a second and I really doubt a bracelet is accurate enough to give the player insightful data. Sure its a really cool device (still not useful) for people starting to learn or maybe little kids competing against each other, but there is a long way until a serious tennis player can benefit from this. I am a software engineer myself and it was always my dream to do build something about tennis. So go for it man..