I did this mostly to improve my cardio capacity and to change things up. I had just finished a 3-1/2 month STS rotation from Cathe that focused on strength, so I decided to focus on cardio. I have really improved in that area with this series (and lost 4 pounds so far - nothing earth shattering, but a nice bonus).
Honestly if the series is too much, you don't have to even follow the rotation to begin with. Do what you can , when instead. You need to push your boundaries yet know your absolute limits with this series.
After 60 days (really it's 63), you can do whatever you want. You can start over (although I don't know how tough those workouts will seem after M1), or you can just incorporate them into your schedule once or twice a week. Really the choice is yours.
Personally I like to change things up since the body gets used to doing the same thing and you're more likely to fall into a rut that way. After this I plan to take a few weeks to just wing it with whatever I want and then maybe start another STS strength rotation trying to put equal emphasis on strength and cardio.
CG (modified) since 6/18/2009
ii, 2c/3a?, med/course, porous (I think), normal elasticity
co-wash: Suave green apple, Deva no-poo, Giovanni TTTT, occasional Deva low-poo
condish: playing with NatPathAV, AOHR,
styling: HE set me up, curl keeper, KCCC, and BRHG