For all its advantages, PropSmith (propsmith.com) has a couple of drawbacks. Each shaft size, including metric equivalents, require separate PropSmiths. Metric sizes aren’t necessarily uniform, either, often requiring a custom-threaded PropSmith for one individual boat. Holes drilled into props are likely threaded metric for European boats, unless props were replaced at some point in the U.S.—or even just one new prop threaded SAE while an original prop still holds metric threads.
In some cases—mostly higher-end boats built in Taiwan—the starboard shaft is threaded in the opposite direction from standard, requiring one PropSmith with a second, left-hand threaded plate. (With normal threads, if a propeller nut is loose it will tighten itself as the port shaft turns in forward gear, but loosen itself completely on the starboard shaft.)
PropSmith also needs enough shaft extending behind the propeller for the threaded plate to screw on. Recessed prop nuts, typically on Italian boats, often don’t allow this. (PropSmith will customize solutions for very little added cost.)