What's everyone's first imressions of Sterak's Gage?

I've been trying to make use of it but I've found a lot of the time the shield isn't going off in fights even when the enemy tears my health to pieces. When I finally did see it trigger it was right as I died and the shield didn't even pop to save me, it just went on CD without doing anything. I can't tell if the item is buggy or if the numbers need tuning.