I took advantage of "local" Appleseed event and came away a better trained shooter.
This is mainly because I've never been to a shooting clinic where the sling was emphasized. When I went through basic training (twelve years ago) we were told not to use the sling. When I went through SDM training with the AMU we were shown how to use a hasty sling, but never used a hasty sling. We used a bipod instead, which is much easier to use.
Appleseed is not a long range rifle clinic, it is not an advanced rifle clinic. You won't learn how to read the wind or calculate your dope.
Appleseed is a basic rifle marksmanship course that emphasizes sling use. It is well worth it to attend an Appleseed clinic. You'll get better marksmanship instruction than I received in basic training.