General

I'd say get the ring, but use other ring until you cap, then switch back to the Kanna event ring.

i will say that 10 mana is not game changing whatsoever (in any boss). Its really insignificant.

Can that 30% int allow you to attack once more? There's your answer.

If you cap regardless then yeah it's worth it, if not then no it's not worth it.

it probably is better if you cap without a cracked/tempest/w.e ring than its probably worth. Some people on here could probably do the math n stuff

Think about it this way, 30% int or a chance to do another attack without waiting...

To each their own I guess.