Two thoughts about the angle unit.
First, except for short cuts it is simply the wrong way to set an angle. Any tiny error at the scale multiplies out to an unacceptable error over the width of a sheet of ply. For example, misreading or shifting the angle by 0.1 degree will cause an error of almost 1/10 inch at the far side. I don't know about you, but my presbyopic eyes can't see 0.1 degree on that little scale and my clumsy hands have trouble noodging the dial that small an increment. When I need an accurate 90 degree line, I use an 18 inch woodpecker triangle, which is good to more like a couple of thousandths over its length.
Second, when you use the angle unit with a long guide rail, the rail provides tremendous leverage around the pivot. No screw-down clamp is going to be able to withstand the sort of torque you can produce with a fairly gentle nudge at the end of a 75 inch rail. You have to expect the setting to shift and recheck it frequently. To me, that kills any timesaving the angle unit might have offered.
Steve