Came across this old post. Wanted to give my experience as a long-time practitioner of this lineage. I feel that this practice is largely misunderstood in the thread. The first few levels of JinGui are made to prepare the body-mind to hold a large reservoir or qi and clean out stagnation. I wouldn't consider the practice extremely mystical, though it has many mystical components. The results are permanent, and never go away once you seal each level. The biggest thing I tell folks who are new to the system is that we are not training to be able to bounce bricks off our ribs or smash tiles with our legs (though those things are definitely fun), we do those things to develop and optimize the way the cells work together. Also as you become more and more visually resilient it increases the feeling of winning in your everyday life which, with the optimized body, enables you to do whatever you want in life. The practice has been essential to my mid-20s. I was an anxious mess when I started, had no energy, no sex drive, and was stuck in my head. This practice first cleared me out, then made me a human. Back never hurts anymore, half my chronic injuries healed themselves, and I never get sick. Society values me as well, which is a nice plus. Every energy worker I go to says my energy body is extremely full. I still have things to work on, and there are some weakness of gaining a lot of power over a short time, but I feel the impact on health and longevity is worth it.
To sum up my point, this is a FIRE practice. It's not a deep mystical tradition, it's more of a very effective intermediate practice to get your "vessel" in order so that you can actually compete in the realm of a deep WATER mystical tradition. Take this metaphor: lets say you were given a boat. It was an average boat and maybe it had some things wrong with it. You'd probably want to fix your boat and upgrade it before you put up big new sails right? Otherwise you'll just get thrown around by the wind.