Cardio and Weights is a circuit workout, but it's as easy as Cathe gets. The cardio is not tough, the weight work is not tough, the ab work is pretty tough. However, it's really fun. I use it on days when I can just barely make myself workout, but at least I can do this. I also like the way exerpts are used in Imax Extreme.
CircuitMax is one of Cathe's toughest workouts. The cardio is intense and non-stop, the weight work is not tough as weight work, but it keeps your heart rate high. This workout is as tough as IMax 1, more or less depending on who you ask.
So, I'd say they're both circuit workouts on two ends of a spectrum. Both are fun and well-done, but they are in different leagues for difficulty.