Overall I'm delighted with the general skill tree and the performance so far of my first fully skilled general.
It appears there's no way to know the precise value of experience gained by Fast Learner. On some adventures we'll be able to calculate it by subtracting the exp value of the adventure from our total. But the value becomes imprecise when loot spotters are involved, as I've experienced already. In adventures where we don't kill all the camps it will be hard to even make an estimate, unless we compare experience gained before and after adding Fast Learner.
With this skill being on the third tier and obviously a matter of personal playing style and preference, I'd like to be able to assess its benefit from one general before giving it to others. I don't expect a precise measure to be available anytime soon! So I'll do my best with calculations. As I already said, the skill tree has been interesting and enjoyable overall, so I mention this in a spirit of constructive feedback.