Unless compelled, the only effect a Fae suffers from contact with iron is that stress and consequenes incurred as a result of that iron bypass their Toughness powers.
If compelled, the only effects the Fae suffers are spelled out in the compel, and are likely significantly influenced by the aspect serving as the source of that compel (with particular note to remember that consequences are chosen by the defender, not the attacker, so one cannot guarantee that firing iron shot at a fae will inflict consequences that even mention that iron).