I'm going through CJ2+ now...its is 95% similar to the CJ3.
If you pay attention in class, and have a half-way decent cognitive understanding of aircraft systems, you'll do JUST FINE. No memorizing useless systems knowledge (example: When does the Bleed Air Duct annunciator illuminate? Answer - When the Bleed Air Duct is too hot. When does the Oil Pressure annunciator illuminate? When its too low.) The ProLine 21 is very capable and will make your life (and training) very easy.
If you know you're coming out this way, call the center and they'll email you a .pdf study guide for the airplane with basic systems & limitation info.