Ok just made an efficient focus and I'm wondering if I'm misunderstanding what they do or if it's a bug. This is what it says when I focus on it:

The enchantment has excellent potency and is very precise. You sense it was enchanted using a red heavy fount with a grooved surface making it major grade with enhanced magnitude. You perceive nominally thick and perfectly clear lines empowering the enchantment. This enchantment was tuned to provide additional magnitude and a moderate increase to mana efficiency to targeted spells.

I invoked the item and cast some TM spells and got a message saying, "A hazy aura reinforces the spell." so I know it's working but I'm not noticing a decrease in mana use at all.

Ok, this must be bugged. Just made two more efficient foci to see if there is a bug or if I was just lacking the proper amount of arcana skill to invoke with the original focus I made. Made one with a minor fount and the other with a major. With over 1000 arcana I tested both to see if there was a decrease in the amount of mana used to cast a TM spell at 100 mana and there was not. Also tried to cast the spells with less mana than the normal amount required and got a message about not feeding enough power.