The Shambala book is good, but it will confuse people if they want to get to know basic Buddhism. Seeing as how, Trungpa, had conceptualised Shambala to not actually be Buddhism, it only became a form of Buddhism after his death. The kind of Buddhism that it is compared to is Pure Land. Sure both of them are forms of Buddhism, but neither are interested in the Four Noble Truths, or the Noble Eightfold Path. Not in the same way that Therevada, Mahayana, or Vajrayana stay focused on developing the path.
Shambala can’t help but be strongly similar to Buddhism, a monk did came up with it, but there are some specific elements that veer way off course.
I’m not saying you can’t use the book as a guide. It has some good stuff in it, but picking up the Pali Canon will be way more interesting, and is actually very readable. The Buddha does a fantastic job of explaining Buddhism.
Sorry to get all preachy. This is typically not my style. I just think it takes quite a bit of reading and digging to sort out the strains of Buddhism so you can best find your way to the path itself.