The forearm is effectively your controlling grip in either: there's really not much difference in control between no grip and one that's flopping around a half an inch in relation to the rest of the rifle. As far as a ban or not, you may be right, but when is the last time the ATF let something like this slide for long?I find the difference in the ability to control the weapon much better with the Slide Fire. Using only your finger while in a shouldered position and bump firing results in no grip, resulting in less weapon control. With the Slide Fire the grip remains on your hand, resulting in better control of the weapon. Didn't you find the grip remaining in your hand to be better for controlling the weapon when you used it?
Same trigger, same action, same physics, all agreed... And that is why it will not be banned in my, and so far the ATF's, opinion.