I'm one of the happily surprised with vinegar sharpening.
And I don't worry about how long it lasts because there's a blue zillion of old USA-made and "Black Diamond" Nicholson's out there for a less than a dollar a pop. They're all dinged up and dirty and dull, but they're cheap and plentiful enough (at this point in time and in my zip code) to only sharpen up once and be satisfied. You just have to shop around to find them.
I'm not using files much of late, but I still haven't re-sharpened a vinegar sharpened file yet. The first one I ever did still cuts great and it has huge rust pits...it just doesn't cut there!
In chainsaw files I only buy German or Swiss-made. Sie sind wunderbar. (find them at the logger supply houses)
The trick (there's a thread or two around here on it): Soak files in 5% acid vinegar (any flavor, standard %) until the bubbles stop fizzing up, 24-48 hours or whatever it takes vinegar is mild. rinse and scrub off the black stinky muck, dry and oil quickly as they will flash rust nearly immediately with any moisture at all. Then go hit some metal with 'em, See if you did it right