They are really nice to have. I ended dong a fret level and dress when I had my mando down to put a pickup in last weekend. I got the stewMac medium/Large combination file, and it has covered every fret type I have seen from ukes to basses. You can shape a fret with simple files. You can even get by just fine for a spot repair by using something home-made. I shaped the tip on a sanding stick to clean up file marks. You could use something like that for the whole process of crowning if desired. It just won’t be as quick.
Also, I’d suggest tapping on the fret to make sure it isn’t loose and lifted before buying a crowning file and starting to level. A loose and lifted fret isn’t particularly common, but it can happen. By tapping on a loose fret with something metal you can tell by the sound (hollow sounding compared to other frets) that it isn’t seated. If that is the issue, the repair is a little different.