Although I can understand the appeal of statistical shooting, I would like to humbly relate that I've been following an approach that is quite different.
I don't know whether it will work for everyone, but I believe that manual focus can be trained similar to throwing darts or basketballs, or playing an instrument.
You have to force yourself to get it right on the first try.
I did and still do the following practice method.
Pick a very fast shutter speed to make it just about the focus (like 1/1000s).
I stand with my camera in front of my belly, arms relaxed and my left hand on the focus ring. I put the lens on infinity between shots to have a consistent starting point.
I pick a target (for starting out, targets on an inclined plane like a bookshelf at an angle or an isolated target like a sharp pencil in a mug are best), I look at it and try to concentrate on its appearance. I then raise my camera to the eye while inhaling, and while exhaling I turn the focus ring in one continuous motion (no overshoot because that is too difficult for the brain, at least mine), stop and press the shutter. Then I lower my camera again, inhaling and exhaling, before doing the next turn. The whole cycle lasts 2-3 seconds only. I do five of the same target, then calmly evaluate the results. Afterwards, I go to the next target, picking a nice variety of focus distances between MFD and a few meters (for close to infinity focus I do rely on the green dot, otherwise I try to ignore it and concentrate on the visual appearance of the target). I will do no more than 5-10 targets a day, and then do something easier for the rest of the day (like shooting at smaller apertures and work on composition and exposure).
The method has the advantage of not straining the eyes so much because they can relax between the shots, while standing there turning the focus ring back and forth around is very tiresome for the eyes, and small differences are harder to perceive than a continuous focus action. You benefit from observing the target with your naked eye and having a short-term memory of it when you see it again through the viewfinder. Your brain learns how much to turn the ring based on the distance (if you prefer, you can also start from MFD all the time). You maintain a healthy breathing cycle and a relaxed stance, both of which make the whole thing more enjoyable, while also giving you a stable platform for slower shutter speeds. You also train yourself to be quick, which is handy for street and portrait shooting. Because you are not overshooting while turning the ring, you will learn to have a sense of the degree to which you missed focus even without looking at the image (like when throwing a ball, you usually know that it will miss as soon it leaves your hand, so over time you will be confident that it hits once it leaves your hand).
It's not that trying to nail focus by going back and forth is bad in itself or cheating, but I find that I'm not able to train myself to get better that way (essentially, it's an open control loop and you never have to make a commitment). I will reserve this for the really hard targets, but while practising I try to make one continuous turn and then stop.
If you try this, I would be interested to hear about your experiences.
