All players in my team have an SA. I lose on purpose on the league before than so they wouldn't lose a star and get them those SA. I don't know if it was worth it, but for example Shadow Striker for my AMC/AML when I am playing 4-4-2D (changing to 4-5-1V) Shadow Striker seems like an awsome SA for this player. Playmaker for an MC is also good, Free kick speacialist is totaly worth it! One-on-one scorer is also a good SA. My DC/DL/DR have Defencive wall/Aerial Defender and my GK's have one-on-one stopper. I don't know if they make so much difference vs the cost of the SA (40-50 skill points), but since I didn't lose a star I got them for free. Now time will tell how much they matter