I can only assume by your post that you somehow think I am saying you are sweeping along the board for infinity .
Like the clubhead, the head of that brush travels in an arc. The idea is you just take your normal golf stroke and brush a portion of that board as it travels in this arc.... Not drag it along the entire board !
A straight line is a straight line - the fact it is on a board 90 degrees to the plane angle intended for release doesn't alter the fact. You are still maintaining a straight line relationship to a straight line. All that the board does is make the plane angle and plane line visually easier to see.
Ok . . . I think this thing would make more sense if you flipped it over where the club swung under it. It would keep the person from having a plane shift through the ball and allow them to go all the way down and be on plane with out disrupting #3 by raising up the shaft. The way you got it set up disrupts the arc.