The Fast Track isn't watered down, it's just way more info than what the ICM is (and includes Enterprise Plus info). The question is more a question of how well do you learn when you get a glut of info given to you. The way to compare it is to consider which you prefer: drinking out of a water hose (ICM) or drinking out of a firehose (FT).
Fast Track is all of ICM plus the What's New class and an additional 2-3 modules.