[Yumyums Inmahtumtums]

I personally don't have one so I'm biased against it but here is my experience:

Solo'd lots from 54+ with epic. I am currently a 59 Barb shaman with rubicite Bp (little league regen). I can effectively lock down 4 mobs and epic dot down without LOSING mana meaning I am effectively between 80-100% mana throughout the duration of the fight.

My main mana usage is root (PE) so in that sense I don't really feel the need to cast spells that take 8 seconds to cast and have a chance at breaking root then damaging me (hp=mana). The only times I've felt it would be useful is if I'm doting the last 10% of the enemies health and that time would be better spent moving on

I suspect it would be extremely useful from 45-56 and then again at 60 when you can solo farm summoning mobs. Aside from that I can't think of many times id rather cast an 8 second nuke versus medding/canni/casting something else.