Yeah their core workout is very good. I'd recommend it. Another good alternative to that though is this one. [ame]http://www.youtube.com/watch?v=8tmN66e8WvE&feature=related[/ame] [ame]http://www.youtube.com/watch?v=ISfOhGqF0Gs&feature=related[/ame]
This is the ab exercises i use, aint been able to do much lately due to injury but when you get into the routine of doing this regularly you will notice a positive difference
Used to do this workout one day on, one off...great results, and you can run through it differently too depending on your level of fitness. At first it was intense and I had to take breaks, then my body got more accustomed to it and I could work it straight through. 15 minutes of work, i might get back to this instead of freestyling ab workouts