I highly value an advanced trainer with career extension over a superior trainer with no special.
If my advanced trainer stops 1 guy from losing a skill point each season, that is like 7 pops for me
Overall though when using the training simulator, you can get a superstar to cap out rather easily. The more the player leans towards SF position the longer it will take to cap.
Besides I don't really want to cap my players all that quickly. Just my opinion.