It works perfectly
I test many SVG files in Freecad with different unit (create with Inkscape), I also test with online SVG fretboard creator to confirm and all dimensions are respected.
Apparently, Inkscape not use unit (just for its interface). beaucause with different unit (mm, in.....) SVG code files is always the same
Finaly, Inkscape SVG unit file does not matter !!! it is always "px * 25.4 / dpi" (25.4 because freecad is always in mm)
to precission, I make rectangular 100*200mm with inkscape, import in Freecad, check dimension....perfect 100*200mm too
Nice work. You deserve your trappist beer (sparingly)