UFB.
Short story: Was project manager years ago for a renovation in DC at the Embassy of the FRG (Germany). The drawings were all metric. Situation Normal: nobody had anticipated that.
The carpenters in DC during that era were mostly all from down in the Shenandoah Valley (now mostly all from out of the mountains of El Salvador: everything changes). Feet and inches of course was all those carpenters knew. It was a problem.
I found and bought up a couple dozen metric tape measures before we mobilized, and gave one to each carpenter, plumber, and electrician on the job. In a single day (ONE day), they were all sold; to the man.
The key was eliminating the whole conversion nightmare. Without having to figure the #@^%* conversion problems (metric-to-standard, or standard-to-metric) it was a breeze. You just rolled out your tape and marked the exact measurement shown on the drawings. And the architect was German so EVERYTHING was exact.
And they especially liked the additive measurements: mm+mm=mm's (doesn't get simpler than that).
And a mm is small enough that it eliminates all the "RCH" kind of fudging. And of course no need for calculating 3/4"+1/2"+3/16" kinds of problems.
They never had to stop to calculate anything: just measure, cut, install. Everyone of those guys (including me) was sold on metric after that.