Geargrinder is a Void affinity rare from the Ogryn Tribes faction. Geargrinder was added to Raid as part of the legendary fusion event for the High Elves champion Pyxniel.
Geargrinder really only has 1 place where he is an MVP, Faction Wars. He is the only reviver in the Ogryn Tribes making him valuable to complete all of Faction Wars with 3 stars on each level.
He can be a solid support champion in any Dungeon as a healer / reviver.
I do not think you would need to take him past level 50 or invest in masteries past tier 4.