This adds to the already versatile and useful Berserker Rage ability, making it a very powerful tool, providing a flat Rage boost, and bonus rage from damage taken. The ten and twenty Rage boost turns Berserker Rage into another Bloodrage, on an independent timer, and allowing much more Rage to be generated from a standing start.
The downside is that it is pretty far down the Fury tree, one step above Bloodthirst, and will require a significant investment into Fury to unlock. A must-have for dedicated Fury builds, but less accessible for Protection tanks.