Is it likewise a powerful conversion tool for atheists?

Definitely. Think about young people who go off to college. An atheist could say to a student, "Hey, I can help you become more rational. Don't believe in religion or any of that other stuff that your parents taught you." Well, that might work to some degree, but it would be far more effective to say, "Did you know that the moral rules that your parents taught you are just in your head? I've got a way for you to get rid of those rules." See, if you reject the idea of God, then you don't have to do any of those things that God supposedly commanded you to do. Atheism can be a sort of manifesto of moral liberation from rules. And the rules that are most objectionable in our day and age are those that basically say, "Thou shalt conduct thyself with responsibility, chastity, mutual fidelity, and so on."