Are Fenris Brood any good?

I love the Tyr's cult because he gives me two units i love: Jormungandr's Elvers and Fenris Brood.

Jormund E are really good as water units. But instead i find Fenris Brood kinda weak. Their passive is good but they are too squishy and they often they can't use it well because they die. They fall super ez in battle in the late game phase when they are unlocked.

Is there a strategy to use them well or they are utter trash?