Pretty much what you do on the opted you do on the real thing.
Kaplan
Depends on the person really. I've heard the "guaranteed to improve your score" But then again I've known people to improve but also to do the same on the OAT after taking the course. Guess its how much you put into the course.
If you have a rich science background, with the motivation to study independently from a course, I would not recommend taking the class. I know alot of people whos scored 380+ without the class. Buy an MCAT or DAT review book, and go crazy.