If character is sorcerer or wizard (with conjuration school) and they possess the feat GSF: Conjuration, I think it would be interesting to let them interact with conjuration items in a unique way.
For example, for reagents that get consumed upon use, maybe the conjurer draws additional strength from the summon focus and all summons are +1. While for summoning times, the conjurer bypasses any negative summon modifier attached to the book.