Now this is just my opinion, but I believe the air file or straight line sander is designed explicitly for straightening long, straight area and long body lines. I have never tried to use a straight line sander by holding it vertically and running it over a curve as shown in the video; to do so would be counterproductive no matter what shoe was on the tool. I think the maximum inclination from vertical for a straight line sander is probably about 30° or so, depending on the circumstance. Basically, what is seen in the video is trying to use the wrong tool for the job, then creating something that will make the tool work for the job, while destroying its ability to perform its primary function, which is to make long straight panels straight.