Using it on the first round is also an effective strategy.
Pair it with harmonize!
R1: Crusade Banner + Harmonize. C11, R8, Ch3.
After 9 rounds, (24 mana), you can summon two Knights of Westlock for only 2 mana!
That gives you a profit of 13 mana, and that gives a good backup in case things go sour.