Is it intended this rune is not scaling? A 125 shield seems pretty weak for a 1min cooldown. I have 272 spell power and 246 healing power, and it still only does a flat 125. It does not appear to apply a crit absorb either.
It is supposed to pulse a shield every 2 seconds, for 15 seconds, does not instantaneously provide a shield, but I did get 8 rounds of shielding.
If it scaled off like 40 to 50% healing power, that would at least be ideal. Most of mage healing comes from spell damage anyway, so it not like mages are going to go full healing power. 30% healing power would be acceptable if it at least crits.