I cannot imagine anything that works any quicker, easier, or is any less trouble to make than one of these. This is one of my case trimmers.
With it I can trim a case in about five seconds. Blade is replaceable if it ever gets dull. Blade is not at 90 degrees to the axis of the dowel, but is very slightly downward angled in order to give it a quick "bite" into the full length hull. A thumbtack in the end of the dowel, even with paper shims under it, can vary the length of the cut hull to suit.