Filing ist not the poor manís alternative to a mill. More often than not sawing and filing is faster than milling. Filing means better workflow - less set up - less swarf - and no razor-sharp chips. Filing is flexibility: Not every surface needs the same precision, not every surface needs the same nice appearance. And milling edges is time wasted.
Yet the work stress is considerable. As with forging or horseback gymnastics one has no second try. Most annoying is the immanent danger of rocking the file resulting in curved or inclined sufaces. So any anti-rocking-aid is welcome.
I have seen a number of filing rests for turned parts still clamped in the lathe chuck; to file flats or hex nuts.
But I have never seen a filing rest for a vise. Perhaps it would be too complex to adjust.
So I started with something simple and doable; which is - by the way - the royal road to any novelty.