nice!I may at some point get shorter leveling beams from Stewmac for guitar and banjo, but for a 24" levelling beam I use an old masonry level, bought at a garage sale for 1$ and trued at home on the same float glass my father has been using since the 70's.
and there's no reason not to use that bar on guitars and banjos, too (i certainly use my 24" beam on guitars).
...although i did find an old big 10" mill file that was damn flat (most aren't) and modded it by chopping the ends off and gluing a wood handle on one flat side of; it gets used for adding fallaway to the ends of fretboards or for quickie spot leveling. so i suppose there is a place for shorter leveling files like that.