My son is living proof that it isn't always that effective :).
My husband and I have decided to let God determine our family size. As my last pregnancy had serious complications, we don't say this lightly. God was merciful and all went as well as it possibly could have. I must confess to some fear, but God is sovereign over all...even my womb.
In faith we truly believe that if this be the will of God, He will provide. The Duggars are an excellent example of how christian faith works. Good for you and your husband!
We’re struggling with this too - I am 41 and my youngest of 5 is 1. I am completely against artificial contraception and I struggle with NFP for similar reasons...still struggling with it - its a trusting in God issue, I think.