Val’anyr Proc details direct from Blizzard

Last week I went over the stats of the new legendary healer mace Val’anyr.  A lot of people have been unsure of whether the proc on this mace is worth the effort and who should get it in their raid. Bornakk was nice enough to give us a good overview of how the proc actually works over in the official forums.

Here’s a quick TL;DR:

• It can proc off both HoT ticks  and Direct Heals (as long as they actually heal the target).
• It has a 10% proc chance and a 45 sec internal cooldown.
• The healer gets a buff for 15 secs that allows them a chance to cast the shield on any targets they heal.
• The shield absorption is 15% of the heal, rather than just what the player received. [This means overhealing will still produce good shields.]
• The shields  stack. Meaning if you have a 1500 damage shield up on someone, another heal will proc another  shield (lets say also for 1500) which would be a total of 3k damage absorption. All heals cast on a shielded target contribute to the shield while the healer is buffed.
• It stacks with Power Word: Shield.
• The shield last 8 seconds and is refreshed on each heal while the healer has the buff.

(Source)
So thats the official word. Now, opinions on over or underpowered?
I know I would be pretty happy to have my pocket healer carrying one from the tank standpoint.