I won this book in a contest, but it had been on my to-read list as part of my research in writing about your family history. Most people who wish to write about their family history probably won't do it as a memoir because a lot of it didn't happen to them. However, there are some people, adoptees searching for their biological family for example, who may wish to do so. With that in mind, I wanted to read this book.
If you plan on writing a memoir, I do highly recommend this book. I don't have a memoir in me (right now anyway), but even then this book gave wonderful advice on writing about real people, real secrets, and what could happen because of that. Always though there was the advice to tell your truth - tell your memory of events (as that is what a memoir is; it's not an autobiography), and be sure there is a reason why you must tell it. The book is inspiring in its stories from other memoirists at the end of each chapter. In that, you get much more than just the author's experience of writing memoirs, but many more.
As far as it's use in writing family history, it's there, definitely. However, I feel this book would be most beneficial to someone who went through something and changed somehow and wishes to reflect on it and share what she learned from the experience. Can that be from learning about your family history? Absolutely. But this book has so much more to give than just that point of view.