I dont have any proof, but my theory is that it swaps con with wis if your con is lower than your wisdom. However there is a drawback in that it only works if your "calm", if this means calm as in able to sleep or calm as in able to enter a guild I do not know.

In regards to if it increase your regen to your max con, or to your wisdom score I have no clue about. But aslong as your con is lower than max(which it will always be after your character grows a bit older) , its always a good edge.