The completion sadhana of Vajrayogini focuses on the central channel (also known as sushumna in the kundalini yoga), by bringing into the channel all winds (aspects of prana, the life energy, that fuels the emotional and mental events in the mind) and dissolving them along with the bija and everything else.
I agree, Kriya Yoga is not for beginners or for those that are not really fully dedicated to spiritual transformation. In practice, that translates to disciplined and really opened heart and deep willingness to surrender to Devi.
I was introduced to four levels of Kriya Yoga practice.
The Second Kriya, as I see it, employs powerful and efficient mudras and bandhas: mula bandha, shambhavi mudra and specific breathing. It is also used as a process for leaving a body at the time of physical death. I spent hundreds of hours performing the sacred techniques until I was allowed to move on to third Kriya. Second Kriya for me is at least twenty times more effective then the first Kriya.
The Third Kriya, as far as I can see, is even more powerful and efficient. It is in two parts and it employs complete mula bandha, shambhavi mudra, bandha traya, retention of breath and of course, a specific kind of breathing and directing of attention. It is a mighty tool, far beyond anything words are able to convey. I must have spent hundreds of hours performing this Kriya alone.
About the Forth Kriya, my Master has said: “This is a way to God.”. And it truly is. It employs powerful combination of aforementioned mudras and bandhas, sacred mantra Aum and retention of breath. Even during the Forth Kriya samadhi manifests easily and effortlessly, what to speak after the Kriya practice.
An authentic Kriya yoga initiation is a must. There are various lineages existing currently on this plane. If inspired, maybe one can seek initiation from organizations through the links: Kriya Yoga Shrine and Library >>
see also : Kriya Tantra