I heard somewhere that the new curved blades give very little extra aerodynamic advantage compared to traditional ones, yet the cost of manufacture is considerably more!
Of course the main advantage would be how much sound you get from it - on an aeroplane it's not really an issue - they're loud anyway and wil make a noise. Submarines are really careful about how much noise they make as it's how we find them! If they can quietly sneak along with the engine running, they're moving and hard to find- an advantage if someone is trying to throw a torpedo at them.