My thoughts on undo:
1) I like it as a feature. Misclicks happen.
2) Each request is just that, a request. You are at the whim of the other player if you are asking for an undo. You had 5 minutes to plan out each action, it's your fault that you misplayed. May your opponent have mercy on your soul! I don't think I have ever denied an undo, but if someone denied me one I wouldn't blame them, I'd blame myself.