End in Sight:
Pablo, why don't you practice it anymore, and what did you get out of it when you did?
IMO, the short answer is that these practices leads to a "fake enlightenment", with a high standard of concentration, health and even siddhis in daily life ***, but that fades gradually once you stop doing the exercises. I read that from at least two long time practitioners. Of course, this might not be the case if you're already enlightened before trying them.
Otherwise, it would be interesting to know how these tummo/kundalini practices could be placed in the insight/samatha map. One wild speculation is that they are a clever method to lengthen and strengthen the A&P peak. Other, that with the energy pipes cleaning up through breath retention, you can skip DN and jump to EQ. As an anecdote, if you're standing up in a fetal position and you inhale expanding your lower-back and hold your breath, all thoughts vanish completely until you exhale.
*** I did that qigong for a few months and so had little results, my experience cannot be taken as relevant