I asked this like, 5 years ago, and got the answer that it was balanced. That said, I'm going for it again.

I think its time that some element of Arcane Focus and the Heavy Quartz Orbs is re-evaluated. Compared to other such magic items:

A) The duration is short and non-extendable through training.
B) Few charges (often 1)
C) Heavy weight
D) Benefit of the spell is low

Are all 4 of these really necessary to balance Arcane Focus? I've heard the "CS buffs are extremely uncommon" as a reason why these must be so prohibitive, but I think for a measly 10 CS (I know about the low level CS increase), this is a bit much. Even adjusting one or two of these would go a long way towards making these more useful. To be honest, the duration might be the best place in my opinion . . . make it adjustable with MIU, but maybe only 10 seconds per rank or something.

The orbs are a pain, but I think the intention was to avoid the situation whereby hunting with Arcane Focus becomes the norm, thus requiring creature tweaks and so forth. But as noted, the orbs are chargeable, greatly enhancing their value, and the spell is also found on scrolls. I think it's probably okay as it is, in my humble opinion.

~ Heathyr and friends