I tested this too and it is fine product. I was pretty spot on perfect line most of what i tested(borrowed from friend for couple days) and fooled around with it.
However. I gonna get one for teaching. I think this is wonderful tool for pool teachers.
It won´t still fix center ball dilemma. Where one think center ball is... and really it is not.
Still even with perfect line some days I miss judge center ball vertical axis. I seem to think it is more to right than it should be. Tool was great for realizing that.
I got some drills that i invented long time ago to fix that and find line of aim . I just need to make them more often to keep my bad habits away.