If you look closely at the parallel guide stops, the pointer is raised above the surface of the extension with the stop surface by about 1/2mm. Likewise, the extension's top and bottom are not parallel, they taper slightly down from the surface of the bar. By having the single screw with a wavey washer, the pressure can be adjusted for smooth operation and holding friction. If support is not necessary, they are out of the way in the gauging position.
I agree on the rounded corners - that was part of my original idea, but in my haste to execute a prototype, I just didn't bother with the extra step.
I used 1/4" thick scrap from router base material. with the width I used, there are 2-1/2+ diameters of solid material surrounding the holes. This exceeds the spec required for rivet holes on airplanes, so I think it should be quite durable in this application. I wouldn't want to make it too much wider as this might interfere with easy operation of the cam-lock lever.
When you mount the tabs, you will have one left and one right hand guide stop.