It is great that you find this book such a useful tool, Hummingbird, as undoubtedly many others on (and off) this forum also do.
For some of us, that it does take BOTA material as its fundament
is important, as it places the book - and how useful a tool it may or may not be - in context.
If I wanted a tool with BOTA-type assumptions, then it would undoubtedly be a good tool. If, on the other hand, I need a tool which clearly explains how, for example, the letter
Alef may intimately be related to the Magician, then as a tool it remains as useful as using a hammer to spread jam on my croissant.
Usefulness of books also depends, to some extent, on whether the assumptions made are consistent with where one is travelling - a roadmap for Beijing may be very interesting, but not very useful during my residence in Melbourne.
The book remains well written and useful
within particular contexts
.