Good thing you made him a merc, that skill, for me, once he maxed out his luck, his weapon he attacked with only got used 4% of the time.
Also, what did you guys make your Avatar's Asset and Flaw? I have gone with Resistance as the asset and luck as the flaw.
Also, when you marry donnel to some girl who has a kid, and make sure he passes on Appitude, which adds 20% to each of his growths rates, it's a skill you do not want to pass up.
