Burner man, I totally disagree. I think you really need to try it before you 'dis' the device.
I have a pretty subtle difference in a couple of my grips I throw into rotation. For instance, I have a left hand grip with the thumb counterclockwise of center-- my WAY weak grip. I also have a grip I use with the thumb more on top of the shaft (neutral) and of course I have my personal favorite with my left thumb clockwise of top (strong). Trackman reveals the amount of closure or openness with the varying grips. I may not know exactly the degrees, but I have a ballpark idea.
Additionally, as for angle of attack, I have left different kinds of divots all throughout my golf life. But generally, each range session is consistent if I keep the same club and don't change patterns. I have come to recognize my 4-5 ish angle of attack as opposed to my 1-3 ish angle of attack and my near zero clean pick off the turf. If you were standing beside me, you too could discern the difference after a while.
Finally, I have a couple different patterns I toy around with on swing plane. I have my personal attempt at slightly out-to-in , down the middle and in-to-out. I can give you a 1 to 5* open or -2 to +2*, or 1 to 5* closed on demand. Now, my standard deviation may be 4*, but I can get it in the requested ball park.
So I can, say, use my neutral grip and swing in-to-out and take a massive divot. I can look at the readings and if the visual result was favorable I can confirm favorable data on Trackman. If not, I tinker around with different variations and hopefully put a better pattern together.
And even if Trackman is not your personal cup of tea, your 99.01% arbitrary number is not fair.
Respectfully,
dsmith