We had a discussion about two months ago about the potential abuse resulting from the combination of Mercurian Magic and Imbued with the Spirit of (Form).
Being able to cast a level 40 ritual every week, without spending a single pawn of raw vis, is potentially game-breaking. Even a level 60 ritual will only cost 2 pawns. There is a real risk of every magus in the game will quickly end up with +5 in all mental stats for very little vis being spent.
(As a side note, finding a familiar related with Mentem would also become impossible.)
I'm going to nix Imbued with the Spirit of (Form) before play starts. It may become possible to acquire the virtue later on, but only as the result of an actual story.