instead of looking at fancy expensive glass nail files or whatever, pay 10$ for the leatherman surge replacement blade kit, it gives a sawblade (you dont need this unless you do) and a t-shank 3 sided file, one of the sides being a ~600 grit diamond file
it files my nails better than anything I've used, and lets me sharpen knives in a pinch, for less than a fancy non-disposable nail file
AND you can put it in anything that takes a Bosch T-shank jigsaw blade (check first, it might be missing a hole now that I think about it) if you need to file a lot of fingernails rEALLY FAST or something
just be careful because it will scratch the fuck out of your phone screen, being a diamond file
you can probably find cheaper diamond files, but it's hard to find good quality ones that fit in this form factor (8.5cm x 1cm)
not quitesure if I should tag this 'knife' but it's in the category of things I wanna chat about and see so i"m tagging it anyhow