Quote from riskarb:
The straddle generates less deltas and loses vegas as the market moves away from neutrality -- the wings generate deltas very quickly, as well as vegas.
Time flies or diagonals are fantastic for aforementioned reasons. My only concern is substituing a symmetric-tenor [1mo x 2mo, 3mo x 6mo] with these lopsided positions -- short one week, long two month. Vertical flies are great in certain applications, but they're reduced to a path-independent payoff. There isn't much to think about. The greeks do invert on 3 moments, but it's basically a P-I bet.
Time flies carry convexity on speed and vol. Good stuff.