Where did I say you were not allowed an opinion? I'm not a fan of anything "synthetic" tool used as a shortcut to learning the correct method from scratch, but as previously noted, that is my opinion, just as it is that the double base is ludicrous and the result of stupid coaching or lack of any coaching at all.
I developed The Bat Jack when a pretty good professional hitter was having issues with his grip and the slot position of his back elbow. He had numerous coaches try to explain and demonstrate what they were trying to get him to do but he could not feel it. When I made this for him and put it on his bat, the light bulb went off and he felt what everyone was trying to get him to feel.
I went forward with developing The Bat Jack because it helps hitters. And yes it is something that you are supposed to swing and hit with.
You claim that this is some kind of a "shortcut" to learning the correct methods from scratch. Well IMO, as a coach, wouldn't you want your players to improve sooner than later? Is The Bat Jack a "shortcut" NO, there are no shortcuts. It just gives your players a better way to feel and understand what you were trying to teach from "scratch"