i never use them.
i would like to see a training hall that could allow the brother have a chance to gain a good trait or remove a bad one. exp boost is nice, but it should be a rather basic function, and its somehow expensive in the early & mid game.
or even remove the weapon expertise from perk system, and add them as a trait, then those sword masters will really master the swords from the beginning because they could always have that trait when you recruit them.
or even gives a very low chance to gift the brother who trained there an extra perk point.
all these changes would make the training hall alive.