I don't have diabetes, but I have known many folks who have including my mom and her mother.
I started the blood type diet for other reasons, back when the original book first came out. so as of this writing I've been doing it for 27 years.
When Dr. D'Adamo came out with his health library series, which this book is part of, I got all of them and read them. He has published on cancer, arthritis, cardiovascular disease, aging (about cognitive health issues), allergies and fatigue, and also managing menopause. I thought they might be useful for sharing with friends and relatives. And I wasn't wrong.
Also at the time there was an on-line forum with hundreds if not thousands of people who had found healing through the diet for many things, and I spent a lot of time looking at what various people were posting about their health issues. Many were sharing how they had used this book and the others in the series to fine tune their management of disease. Many reported cutting their need for insulin by a significant amount in a very short time using the diet, or in some cases being able to get off insulin altogether.
Each of the books in the series recommends not only the diet, but specific foods in the diet to emphasize for helping each condition, as well as specific foods that exacerbate the condition. In addition information about supplements and other things you can do that will help manage or heal the condition is also included.
I highly recommend this book if you are battling diabetes. And you might want to get the book that started it all: "Eat Right 4 Your Type".