Indeed, your right to be skeptical, no person should take anything on faith...
A few things Blabbate...
First, i use a slow cadence on every movement, this reduces momentum, and creates a deeper level of fatigue within the muscles, which in turn also produces greater vascular benefits.
Doug Mcguff explains it better in this short interview, listen careful to what he says to the local cardiologists comments http://www.youtube.com/watch?v=1FrP5k2_B9Q
Secondly, My workouts are fast paced, literately, its from one movement to the next, just enough time to resist mentally, then boom!
My workouts last a mere 12-20 minutes, however this is not important, its the quality of work that's important. I find myself sometimes lying on the floor for 10 minutes after these workouts.
My resting heart rate it better than ever, even at 235lbs, its usually sitting at around 50 bpm. Years ago when i ran or cycled almost every day my resting heart rate would have sat at around 65-70 bpm (and that was at a lighter bodyweight). Moreover, i suffered greatly with knee, hip and connective tissue problems when running and cyclying, as steady state exercise is "low intensity high force exercise", as opposed to H.I.T with weights which is "high intensity low force exercise".