[thejeff]

The about Blood items is that they're cheap. Once you've got a good Blood economy going, you'll be pulling in far more slaves per turn than gems. Ritual spell costs reflect this, but item costs can't, since they're tied to the path requirements.
Even things like Armor of Souls (25 slaves) can be spammed, which you'd never do with a 25 (or even 15) gem item. 5 slave items are practically free.
Flesh Eaters are good anti-thug weapons. Ring of the Warrior is good fighting high-def thugs. Boots of Youth spamming is practically required for Abysia at least.

But yes, Blood really shines in the summons. Many blood nations also have national blood summons, usually sacred, that are even better than the normal demons.