Karen,
SFQ is primarily geared towards health. Other forms of Qigong exist but from what I can deem, Level 1 of SFQ is geared towards the individual - you and health.
Active exercise's are as best I can describe it used to 'move' the energy in and out of body to clear any blockages. This would be the equivalent of blowing through a garden house half full of water and seeing the water come out the other end.
You should always consult with your doctor before doing any form of 'exercise' ... but let me tell you my first experience with Qigong. When I was watching the tape the first round through, I thought, ah, piece of cake! That's until I was doing the exercises and when I attempted to close my eyes to focus ... I was all over the place, no balance whatsoever. Guess that's why I never made it to the world gymnastics competitions! 
I managed to get through five minutes of active exercises ... my point was, what was my point ... oh yeah, not to go hard on oneself at the beginning. If your doctor gives the ok, start out doing just a few minutes per day... the body has an amazing ability to adjust given time.
As for Ken Cohen's program, cannot comment on that one ...
As you've stated, there are many forms of Qigong out there. SFQ was my first introduction to this ancient practice and Chunyi Lin does a 'fantastic' job conveying the basic's to give one understanding but also quench one's thirst to want more!
I'm no expert at this yet, I'm just a newbie with a fasination to want to master this truly remarkable skill.