This book is better than some other books.
It tries to pull the Quantum realm into the Spiritual through physics/mathematics/sound waves. The future.
Also, “The Gateway Project” was preceded by a document Called The Emerald Tablets of Thoth, which gives a better road map to astral projection.
https://www.horuscentre.org/library/Hermetism/The_Emerald_Tablets_Of_Thoth.pdf