I realize it's not M/L PC,,but I use a worn out for my other uses) EZE-LAP Diamond Hone to sharpen flints.
I use them in my other restoration work frequently and they do wear out to the point that they don't cut as well as I'd like them to on steel.
I put them aside anyway (never throw anything away!)
I tried one on a flint one time and found that it shaved the flint remarkably easy.
Like filing hard wood or ivory with a very sharp/new fine cut file is about all I can describe it.,,and this is with a 'worn out' EZE-Lap
I've used both the Black (course) and the Purple (Medium) on flints and they both cut well.
These things...
https://www.ebay.com/itm/EZE-Lap-Economy-Diamond-Medium-Grit-Diamond-Hone-and-Stone-Sharpener-EZLLM-NEW/223282271246?hash=item33fca9140e:g:JGsAAOSw32lYthjfI usually sharpen the flint while it's still in the jaws. Just a few swipes accross the edge sharpens it right up to a nice even knife edge. You can quickly change the angle if you like as they cut the flint fast. I've used them to reshape the flints on top and bottom to get rid of bumps and uneven surfaces so the jaws can get ahold better too.
The flint debris you remove is just dust,,it's that fine.
Hide the plastic gizmo in your buckskins so you don't look out of place and turn your back on the other shooters as you sharpen your flint. But it works fast and clean and doesn't destroy the precious flint any more than necessary to produce an edge once again