Developing an Inferno mage hero.

The magical power for the skill in the Prime Magic branch simply adds to the hero's magical power. That is, all spells and attacks of creatures of all schools of magic are enhanced. I usually take this skill with a mage, as I use spells from different schools.

So, is it worth taking Prime Magic instead of Fire Magic?

And I'll add a question here about Fiery Determination. I haven't used this spell very often. It seemed to me that it doesn't work very well...or am I just mistaken? Maybe it's worth taking Forward! or something similar from the battle cries instead.