I've seen that a lot of guys are suggesting that mental traits are important, but I'll have to disagree.
Maybe they aren't completely irrelevant, but I'm sure they would only come in play if you have two players with the same free kick stat.
This is my belief as you select DIRECT free kick takers. I doubt it has anything to do with decision making as the goal is pretty apparent - either aim at the corner or blast it full power.