The new Manastorm shield

So as you guys know, this new item is coming out as an conqueror drop. https://i.imgur.com/K5cFXau.png
I instantly thought about Divine ire with this. But does that even work ? It's a channeling skill so when does it consume the mana ? Does it consume mana when i press the button, or when i release the button?

Well, we can’t really know until it gets dropped and tested, but “when you cast a spell” should function as exactly as it says, 100% of casts will drain 100% of your mana and grant the applicable damage bonus.

It seems targeted at attack-based lightning damage builds. You cast any spell, get a 4 second buff, and have up to 4 seconds to fill up your mana pool again. It should also work for traps and mines. Anything where you casting is not your primary source of damage.

It will probably grant a non-stackable buff that will either overwrite itself every cast or only grant the greatest damage bonus from mana. I suppose it could simply calculate the damage based off the total mana consumed this way within the past 4 seconds. I don’t know enough about similar mechanics to say for sure.