Insightful Earthstorm Diamond

A druid using mostly HoTs should be casting on average 10 times per 25 seconds, which would mean this is equal to about 12 mp5. With a higher action rate, say 10 casts every 20s, it'd be 15 mp5, but that's unlikely to happen that often. The nice thing is mana return should scale with activity rate, so the busier you are, the tougher the game is, the more the returns on this gem.

Avoid for healers using mostly slow casts - priests who rely on PoH or dreamstate druids might be better off with the +healing metagem.

It takes 2 of each gem after the patch. All of wowhead's item descs have been upgraded to reflect their new stats in the patch.

The mana return is ~300 and (as a VERY rough statistic) occurs 10% of the time. I compared it with netherwind 8/8 procs for testing purposes.