Steiger started writing for Fate magazine back in the 50's, and in the 60's and 70's he was extremely well known as a popularizer of various mystical and occult subjects, and as a “psychic researcher”. A prolific writer, he has produced over 150 titles. This brings me to one point that I think I should note here … there is no way that Steiger could have had in-depth practices in the wide range of subjects that he wrote about, so frequently his books are more “reporting” than systematic expositions of the inner workings of a tradition, practice, or group.
In the case of Kahuna Magic Steiger's familiarity with the the Hawaiian “Huna” system comes almost exclusively from an old fellow, Max Freedom Long, who had contacted him in 1968 and convinced him to produce a “popular” volume synthesizing a lifetime's worth of research, which began with the material and concepts that he was introduced to by William Tufts Brigham, the retired director of a museum in Honolulu around 1920.
One of the points that Steiger makes several times through the book is that the native Kahunas “jealously guarded” their teachings, and only would pass them along father-to-son (even specifying that it had to be a “blood” son, not just some favored youth). Due to the colonization of the Hawaiian islands in the 1800s and the destruction of the native culture, by the time that some non-missionaries decided to take a look at this knowledge, it was hard to find.
If you notice a trend here, it's that one old white guy who'd studied a bit of the native culture passed on what he'd found to a young enthusiastic fellow, who (when he'd become an old white guy) then passed it along to Steiger. There is very little here which is explicitly sourced from a native practitioner, and much of it appears to come from “linguistic studies” where Long tried to wring out of the words used in the native language some sort of belief system. Frankly, much of what's laid out here has resonances with Theosophy, or even the teachings of Gurdjieff, which, given the lack of direct indigenous practitioners' input, is a bit of a warning flag as far as the authenticity is concerned!
That being said, the system presented here is fascinating. Most notable is the concept of the individual having three souls (operating within 3 “bodies”), which reminded me of the Ba, Ka, and Akh in the ancient Egyptian view. Unfortunately, the concept of “Lemuria” creeps in here as well, and Steiger (or perhaps Long, it is sometimes hard to tell) postulates the Hawaiian culture pre-dating the other ancient cultures and providing a template for a wide array of belief systems. It is a shame that that sort of over-lay works its way into this, because the bits and pieces here have really remarkable parallels with various other traditions and lines of research. One of these is the idea that the “present” isn't a point but an averaging across a wider window, allowing influences to appear both forward and backwards without having a hard causality. Another would be a psychological model where “spirits” dislodge and get associated with the wrong body, bringing with them the specific baggage of their former place.
I guess there is a rather large literature looking into “Huna” (I actually ordered a couple of books to follow up on this), which would be all that more compelling if there were more input by traditional practitioners of the religion. At worst, this is a very attractive fusion of a wide array of western mystical threads with some specifics of the Hawaiian culture, with the possibility of being a rather remarkable approach to life.
Somewhat surprisingly, Kahuna Magic is still in print forty years past its introduction, so it should be available (at least to order) from most book stores, and the on-line guys have it, of course. With the caveats raised above, I recommend this as an interesting look at a tradition that is still somewhat obscure.