When I got my first Thoth nearly 30 years ago, there were only two books available in German: The Book of Thoth and Ziegler's Mirror of the Soul. I liked the obvious esoteric depth of the BoT and started studying it at once. But I also liked the practical applicability of Ziegler which allowed me to do readings right away! I noticed and wondered about their differences, but it was not until much later that I learned about the dramatic development which had split the world of the Thothies in two.
In a nutshell, somewhen in the early 80s (I believe), a Jungian shaman called Angeles Arrien did the unthinkable: She published a book on the Thoth based on an intuitive understanding of its symbolism, that is, without paying due respect to Crowley's genius and, even worse, without taking the intricacies of Crowley's elaborate system into account. It goes without saying that Crowley purists abhor her book to this day, but many others felt that it had for the first time opened for them a gate to the rich symbology of the Thoth, plus the book proved useful in readings. Other Tarot authors soon followed in Arrien's wake. Most notably Ziegler, a spiritual counsellor whose books I found helpful in my own counselling sessions, especially when working with groups. Also, among others, Wanless, Tarantino (my favourite besides the BoT), and later Bürgin and Fiebig.
It took them quite some time, but after they had finally got over the shock and found the necessary confidence, the traditionalists struck back: DuQuette and Smulkin wrote books that adhered to Crowley overall, but dared translate his own, often rather unintelligible commentary on his deck to something that most intelligent lay people could cope with.
Banzhaf occupies a position somewhere inbetween, it would seem. Many Thothies more ir less respect him despite the considerable liberties he took; but at least he represented a step away from the dreadful blasphemy commited by Arrien and her followers.
So, to this day, the two approaches to the Thoth are classified by the Crowley purists as right and wrong. Based on my own experience with the Thoth, I beg to differ. I prefer to call them intellectual and intuitive. Scholarly and empirical. Yang and Yin. They are there for a reason, and there is value to be found in both of them.
So, Thoughtful, if you feel you resonate with the book that is the topic of this thread, I would suggest you get it. Perhaps buy one of the books approved of by the trads additionally. Eventually, you must find out how the Thoth wants to communicate with you, anyway.
Hope this helps.