Spell of each kind - does it mean one spell from each magic school? (one from chaos, one from distortion, one from order) or all spells?
If all spells - WOW - this is a real MUST, (the shield was somehow useful, but well, not as much as all spells
)
I remember that I used to choose Sorcerror/Conflux in HOMM3 just for the reason that you got all spells learned if you got the GRAIL.