Seminal, but a little dated. The purely working beekeeper might not have time for it because its biological concepts are somewhat breathtakingly mistaken in some matters that today we take for granted. Remember, the book is 15th century. In those days the genders of bees were not yet understood, nor even their castes, nor were the roles of pollen and nectar. Furthermore, the black letter is a bit heavy on the naive modern eye, and the wording is practically unbelievably cumbersome, as you might gather from the title, abbreviated here.
Natheless, for the thinking beekeeper, the book is worth a good scan, and even a read. It is not for you and me to sneer at a substantial book printed just a century after the death of Gutenberg.