I'm not really interested in isometrics or dynamic tension, but I think the video speaks to the mind-muscle connection that many bodybuilders refer to. I noticed that I naturally and automatically became more focused on the muscles worked when I slowed down my rep speed to about 6-8 seconds. The exercise then became less about moving the weight up and down, and more about working and really feeling the muscle. In so doing, I think I reached MMF at a more granular level than with more "conventional" rep speeds. I suppose isometrics and dynamic tension are perhaps a natural or logical extension of slowing down, but I prefer the middle ground.
I agree. Free weights force your muscles to 'balance' the weight. I believe this 'balancing' uses smaller, otherwise unused muscles. I believe these smaller muscles affect muscle tone. Balance on one foot without schools on ... feel all those smaller muscles in your foot trying to keep you balanced.