I never take the Plate or Mail skill perhaps because I don't understand the wording on it. Do you get full normal armor benefit AND an additional bonus to it for the skill? I thought at first you'd get say 5% of the bonus of Plate. It's like "Why bother?" Now I realize I probably mis-understood it and it's Plate Armor Bonus +5% (i.e. 105% of the normal plate armor bonus)
If that's the case, it changes everything and almost makes having a class that must buy (plate or mail) a better bargain than those who just have it included.