Incanter's Absorption worth it?

Is this Incanter's Absorption a must talent?
The increase is 20% absorb added to damage.
This means about 500points per cast for 10secs correct?
Considering the mana cost and the lack of control (although once youve raided enough you know when you will be hit with elemental damage) Im not sure its worth it.
I presume using Mana shield as arcane considering our mastery is a little iffy at best.
I can see it being used for absolute maxing of output, however I generally prefer some of the other functional talents, Ie speed boost blink, silence CS.

Overall its not to hard to keep it up for many fights but my uncetainty remains, am I underestimating it or is it a must?
I usually throw up shields when moving and I've already casted barrage or I'm in a burn phase and I don't want to clear my stacks. Mage ward also works with it, negating fire, frost, and arcane damage.
on certain fights, on tank and spank's youd have to cast like 8 arcane blasts under its affect to make up for the 1 arcane blast you missed out on because you used a global cooldown. But on like omnitron when your running, or nef when your in transition its very good.
I keep Mana Shield up at all times and use Mage Ward when one of those 3 schools of magic will be involved. like with the elementals wandering around the Ascendent Counsel's room.

I see alot of aoe and splash damage and if using mana shield to absorb a little bit of it can help the healers even marginally then I'd do it even if Incanters Absoprtion weren't an issue. At least with the talent I get some Spellpower out of the deal.
http://wow.mmoscholar.com/2011/06/02/incanters-absorption-discussion/

Read this.

Use it during movement, or during Glyphed Arcane Power, where Mana Shield costs no GCD. It is a situational dps increase, but still a dps increase, over different talents.
I use it over Nether Vortex, since a tank should always have an attack speed slow up.
Its very situational. I like it on omnitron defense system. I dont like using mana shield too often because it does drain precious mana. But magmatron will throw out raid wide fire damage and archanotron throws out arcane so you can toss up mage ward (with glyphed AP for no GCD loss) and gain like 1200 SP. Thats big and leads to some epic burst as well as making some friends with the healers in the group.
Doesn't seem like a must. Guess I'll see in 4.2 raids. If its elemental damage all over the place it might be worth it then. Also probably with some 365 gear, mana will become less and less of an issue.

Cheers all
I don't really get the 'mana less of an issue' part. The more mana you have, the longer your burn phase can be, and the better your regen is during conserve phases, allowing more AB stacks.

I take the talent, though. It's situationally useful, but whatever. Still useful.