Requirements: None. Only certain FA characters have it, like Shaak Ti on Jedi Temple, or Vader on the Death Star. (If the character's description makes no mention of Q3 or 'Attack-Defense', then he/she probably doesn't have it - but if you want to be absolutely sure, look for a triangular mark on your saber style indicator.)
Pros: You cannot be flinched. So long as you have enough FP, any shot that hits you (except shots behind your blocking arc) will be blocked, even if you're in a state where you would normally be unable to block. (I'm not sure if standing still will still leave you vulnerable, it's been a while since I tried that. Also not sure about how it interacts with slap.)
Cons: Honestly, after 1.4 introduced flinching, I'm not sure there are any. (Unless your class doesn't have saber defense 3 - swingblocks, which Q3 automatically performs, cost more FP than normal autoblocking if you don't have defense 3.) Before that, Q3's main weakness was that your swing could be interrupted when you would have preferred to just sacrifice a bit of HP to land your blow regardless. Now? Your swing's going to be interrupted either way, but this way you get to keep swinging uninterrupted and undamaged until you kill the target or run out of FP.
