SA are not useful...They hardly make any difference and cost a lot of skill points...It will be much better if you assign the skill points to his attributes rather than training him SA...
And if you Striker is good in scoring goals from free kicks he will score without the Free Kicks SA too...Further more you don't know how a players performance will be effected after training him the SA...
I had an MC how was scoring more than 1 goals per match, I trained him Playmaker SA and now he has only scored 3 goals in 13 matches......