I bought this for my first custom guitar build, because I was a little worried about smashing my fretboard when fretting my instrument.
It fits over all fret widths and heights (I used very low frets, so that was lucky) and had me slightly less worried about accidentally bashing my fretboard.
Even if you're a experienced guitar builder or repairman this can be useful, just to ensure that you won't mess anything up. Recommended.