It's rather underwhelming so far. The proc does like 0.6% of my healing.
According to Ghostcrawler:
Estimates of Bryntroll at 8 to 10% of dps seem exaggerated to us. Something at the 3 to 3.5% seems more typical. It should be eminently possible for healers to get 3 to 3.5% healing out of Trauma.
I'm not sure what data Ghostcrawler is seeing, but I get nothing close to this. And I'm usually healing tanks, so it should be hitting the melee DPS as well.
The worst part is that [Trauma] is pretty much the only upgrade for a healing paladin in ICC-25. The only other alternative is a sword with hit rating.
I hope Blizzard takes a look at this weapon and upgrades the proc effect for paladins.
As well, they really need to drop an alternative weapon type that paladins can use. The other healing classes get daggers and staves in addition to maces. Paladins can use caster swords, but Blizzard always seems to put hit rating on the swords, restricting the swords to the DPS casters.
Edit: I forgot to mention that in addition to being a lackluster proc, effect-wise, it also lacks flash, which is a very common complaint for healing effects. In comparison, [Nibelung] spawns Val'kyrs to smite your enemies for you! Why does healing never get the cool stylish effects?