Step Blast is an hour long step cardio routine, which features three routines gradually built up and then repeated 4 times to get your heart rate up, before moving onto the next. After learning and repeating all three sections, Cathe then puts the whole thing --all three routines-- together, one after the other three times, and at the end of each repetition she adds an interval blast, before moving right along into the second repetition, etc.
The music is great, and this is one of my personal faves.
Imax 2 is a tough step interval workout. You learn and repeat a very basic short step pattern 6 times, this is your cardio section, then Cathe leads you into a tough, high impact (usually) interval for a minute (approx, because she plays with the concept of a minute quite loosely at times!) which takes you to your anaerobic threshold. Then she lets you have half a minute to get your heart rate down before launching into the next short step routine and the next interval blast. There are 10 interval blasts and step routines all together.
The music is awesome, as is the choreography and this is held to be Cathe's most popular step interval workout.
In my opinion, your collection needs both of these workouts, unless you have problems with high impact work, in which case, leave them both well alone!
Clare