I've been doing joint mobility or daily range of motion training (DROM) for about four years now. As an instructor, I am mostly familiar with the CST material and protocol, but the Z-health is a spinnoff from that. I have seen the Z-health R phase material though, and it is good. The full Z-health program has evolved in more of a rehab direction, and integrates some bodywork now, I believe.
I have not seen the Magnificent Mobility material, but one difference as I understand it is that MM teaches mobility in the extremities, but stability in the torso. CST (and Z-health, too) integrate movement in all possible ranges of motion, coming from a belief that if it CAN move, then it SHOULD. This is not to say that we don't want a stable core - on the contrary - train the core to be strong and stable, able to resist rotation and absorb and retranslate force in multiple directions. However, when it comes to unloaded range of motion work, however, the core needs to stay mobile. Only thru movement will sinovial fluid and nutrition be pumped into the joint. Without movement, joint salts will begin to accumulate and calcification will begin to occur. If a range of motion is not used, the nervous system will limit your ability to use that range of motion voluntarily. Of course, unforseen events WILL take you into that range of motion sooner or later, and then you are screwed.
I love training for all around elite athleticism (well, as much as I can hope for on very limited time), but if I had to limit my training to only one aspect, it would be my joint mobility. It is the element of fitness and health that is most neglected or misunderstood, but it is able to deliver the biggest payoff to your (or your clients) quality of life. Good strength or endurance may help you out in your daily life once in a great while. Same for agility, balance, power, etc. An improved hormonal from profile will certainly help health and longevity, but you can't really feel the difference. However, smooth, pain free movement effects every aspect of your daily life. As the old adage goes, you are as old as your joints.
DROM training is excellent active recovery. You learn to release residual tension from training, and troubleshoot your body prior to training sessions. You will see an improvement in your workouts as your movement efficency increases. With all of this said, if you decide to start any DROM work, don't make the mistake of just doing the reps like any other exercise. Go slowly, even slower that shown, and really feel where the tension is being held, and let it release. Those who have tried any of these programs and claimed that they did nothing for them undoubtedly blew thru the program with little consious attention. Also, don't expect instant results. No one walks into a gym for the first time and expects to get their clean from 65 lbs to 300 lbs within a month. Full recovery of range of motion will take patient work.