Unfortunately the ring is useless. Also the (+ weapon damage) enchant is the worst enchant to use on any other melee except for druid. Not even other hybrids like Ret or Enhance noticeably benefit from it.
It has something to do with how the weapon enchant is coded for feral. It cannot be adjusted for AP conversion either, as you will notice the spell power gained from it is not proportional to agilty/ap. We tried to reverse calculate the value using this method and it dose not work.
I brought this information to Fx (respected Xpoff theorycrafter) over a year ago trying to work out why I was getting these results and our best guessed conclusion is that the enchant for druid is added before the multiplication of the formula. This is only the case for enchants applied to the weapon itself.
For example;
Druid-
weapon DPS + enchant x attack power (+ misc. versa and what ever other wierd sums they put in)
All other melee-
weapon DPS x attack power (+ misc. versa and what ever other wierd sums they put in) + enchant
For the druid all other +weapon enchants or items like the ring mentioned act the same as it dose for other melee.
Obviously iam not great with math and this is not exact formula shown, but you get the idea.
In short the formula for ( +damage to WEAPON applied to weapon only) is broken for druid.