Some player reduce slightly the training speed after teaching the 5th star, whend they reach the 6th the speed is reduces again.

Did you test him tanking free kicks on the match?

If he scores Why waisting 50SP on a SA, that is more that 3Q levels, you Will need around 40greens If he is the Best of the trainers
If he dont, it is not the SA that Will put him to score more from free kicks.

But you decide, what is the Best.