Ready, I've explained the differences between Flex/Core and Momentum in this thread:
http://www.3fatchicks.com/forum/showthread.php?t=159213
However to get the full benefit you really should join meetings (depends on your area for your weekly fee most areas running free registration right now); Monthly Pass $40 a month for boths meetings and e-tools online tools (not available in all areas); online (running a free 1 week and then $65 1 time fee for 3 months and $16.95 each month thereafter); or see if the AtHome program is available in your area I think it is $100 for all the materials you need to do the program properly.