Harner learned shamanism in Latin America, specifically in Jivaro (Shuar) with taking the Ayahuesca. It is therefore a very special present and shamanism we also rooted in a culture that may seem very distant from ours and very difficult to practice in our daily lives. Although the methods he proposes are using shamanic drum or rattle, all the trips they offer year are related to beliefs Jivaro which can really hang if one already has his beliefs to himself, because the trip will be oriented according to these beliefs.
So this book is a real work of anthropological research but on a very specific type of shamanism that will delight those who are interested in shamanism of Amazonian peoples but will not match those that would like to practice shamanism home and who have their vision own spirituality.
He sometimes referred to shamanisms on other parts of the globe to make comparisons. In short a good job but rather to learn to practice that (except obviously if that's what you want to explore shamanism).