I'm not quite sold on Force Hammer. There are some books that I include one or even two, but mostly in Forcemaster-books. For the same amount of spellbookpoints (or even less) I can include a Hurl Boulder, which has the same Slam-chance, but one die more against creatures. It has one fewer die against conjurations, but I believe that a Force Hammer always comes short against conjurations that really matter. 8 dice of damage versus a Wizard's Tower? That's 7 health and 3 armor. Probably won't kill it. I just wasted 9 mana and 7 dice on the enemy mage. Battleforge? 6 crits on 8 dice? May work. But it could not work as well. When it's really important to bring a Battleforge down, I'd rather use 2 Geysers for 8 mana and 12 dice. They'll probably give me my 6 crits.
(Disclaimer: Maybe I need to sacrifice some dices to Akiro.)
Force Hammer is ethereal, but gets his 2 bonus dice only against corporeal conjurations. Maybe it's better to just cast 2 Invisible Fists against something incorporeal. That's not too action efficient, but if you don't want to spend 2 actions on that threat, it probably isn't dangerous enough. You're better off ignoring it.
But when you manage to kill off an important conjuration with just one Force Hammer, it may grant you a HUGE advantage, that's right.