Ideas and suggestions.

The item is good, but it should be noted that in Heroes of Might and Magic V, there is no mentor by default in multiplayer maps and most of the random map generator templates. Plus, the cost of changing skills is simply exorbitant (considering the randomness) and is only justified in the very late game. That is, if you introduce a mentor in Heroes of Might and Magic III, it is not clear how balanced it will be. But for single-player, it would be a good feature. Especially in campaigns, so that you don't have unnecessary problems due to poor character development.