Three things make the Empire great, faith, steel and gunpowder! - Magnus the Pious
The Empire now have monstrous cavalry in the form of demigryphons. And only knights of the inner circle my ride this fearsome creature. its said that as a final challenge they have to go and tame one demigryph before they are allowed into the inner circle and that's why they are so few around in the old world, many never survive the taming of this beast.
This unit i see also as a common choice or standard choice in every empire players list. The demigryoh 3 attacks at strength 5 with armour pierce makes the opponent roll saves at -3. So with a group of 3 knights with full command they will have 13 attacks at -3 when they charge (if the knights still have lances). And with a formidable 1+ save they are really hard to kill. I'm currently setting up a unit of 3 of theis for my army and ill post the pics when they are done.