Well, to be honest, the argument about the advantage of metric system over imperial (even though I personally prefer metric system) on Shipbucket is somewhat academic since the
Shipbucket scale is based on imperial scale after all (1 pixel = 6 inches or 1/2 foot - meaning 0,1524 metre in metric scale).
On the other hand, personally I find it easier to divide by 20 than by 16.
(And since there already is a "Swordbucket" that uses the Gunbucket scale of 20pix/inch. then IMHO there's no point in increasing number of "official" SB scales.