It's not particularly viable as a constant damage output as, say, a Warrior would break your shield with 1-2 hits, and you wouldn't be able to utilise its potential since you have to wait until the http://wotlk.openwow.com/spell=6788 debuff fades from you/your partner. I can see this talent being used mostly against Rogues as they make lots of attacks so you'll have the constant nagging damage factor on them, but Prot Warriors have a better version of this talent -- http://wotlk.openwow.com/spell=58874 -- meaning that every direct physical attack will be returned at 20% of its power, which actually works wonders against Rogues, but you would have to, again, wait for the http://wotlk.openwow.com/spell=6788 effect to fade before making use of the talent.
http://wotlk.openwow.com/spell=47535 is insanely useful in terms of not going OOM, but if you've already gone OOM, you can still put shields on you/your partner and get the 3% mana back even if it gets dispelled(!), which makes this talent invaluable for a disc priest, as it can make it very hard for your opponents to outlast you mana-wise -- you just keep bouncing back without drinking. Put 2 points in it, you won't regret it.
Also, and don't take this the wrong way, but you're really overcomplicating it, these builds are long-established and aren't really subject to much change, so coming up with your own can prove to be a bad idea. A better idea would be go have a look at some of the higher ranked priests in the ladder and copy theirs as they're probably using one that's been there for years.
Good luck