I actually switched to the Ian Knot specifically to handle the stiffer leather laces of boat shoes and boots. Previously, getting a knot in leather to hold was a miracle and I would slip the shoes on and off (causing unnecessary wear and tear) just to avoid disturbing the knot. The Ian Knot allows me to treat leather laces like any other material and has extended the life of several pairs of shoes as a result.
I will say that I cinch the knot tighter with leather laces than any other material because, like you mentioned, they are fussy.