I have one and love it. It is my independent witness. Guys on your squad full of advice? You stopped. You were behind it...
You know they are often FOS but they mean well. The ShotKam isn't guessing. If it shows you were behind it, you were. If it shows you stopped the gun, you did. If it shows your hold point too low, it was. If it shows the bird got away from you and you had to play catch-up, then that is what happened.
As for "why", it can also be insightful. If you stopped the gun, you were probably checking the gap. If you are occasionally over it, you probably lifted your head or mounted poorly. If it got away from you, move your hold point.
You can review the shot on your smartphone right after the shot if you like (though that would hold up a squad if you did it often.) Auto record, power management and controls in the app are done very well.
I find it a very useful tool. At about the cost of 3 lessons, I see it as good value for the money spent. (Don't skip the lessons though.)
To my dismay, it has not done much for early cataracts or slowing reflexes.
Rob!