I've been aware since age 4-ish that I saw the world (and people) differently than most, and I've been a seeker in earnest since high school. Over the next 20 years, I was always on the lookout for anything (Psychology, Biology, Sociology, Spirituality, etc.) that could explain why I was different than most people or why I felt I was on some sort of quest. I discovered the Michael Teachings about two years ago when I was drawn to seek out anything I could find on "Old Souls," and found the Michael Teachings through a self-help book by Thayer White. In it, he strongly recommended the Yarbro writings as a source of research and learning, as over the years he'd never had a major point of contention with them.
I picked up a copy of the first book, read it, and agreed - the book seemed to firm up a lot of conclusions I'd synthesized from many sources over the years. So I picked up the other Yarbro books as well. MMfM and MP also had a lot of good material, but MftM seemed to wander a lot and was more vague in nature. I picked up Shepherd's book later, but by that time I'd devoured much of the website's contents, so a lot of it was repeats.
These days, I use Soul Age and the Overleaves as a system for personal growth, and for understanding and helping people better. I also appreciate the glimpses of what comes after reincarnating on the physical plane ends.