If you speak English and are interested in Bektashism, this is basically the only major academic source you have. It's a great overview of Bektashi history and practice, but is greatly undermined by the fact it was written in the 1930s. The book captures a moment when Bektashism's future looked bright and the order was being standardized and formalized more than at any point in its history, so many of the conclusions the book reaches and predictions it makes for the future did not come true. So much has happened to the Bektashi order since the 30s -- like WWII, the closing of the Cairo tekke, banning all religion in Albania, the opening of Baba Rexheb's tekke in Detroit, the collapse of communism in the Balkans, and the influence of the Iranian Revolution on Shiites across the globe -- that a new book is very sorely needed.