This is definitely required reading for everyone, not just leftists or anarchists. The main takeaway is that advocating nonviolence exclusively, rather than a variety of tactics, is used by people of privilege (especially white people, and that includes white anarchists) because they don't want to feel uncomfortable or actually challenge any of their privilege. Also that nonviolence is largely ineffective at convincing the state to do anything, meanwhile violence tends to actually produce results.
I bought a print version through my local bookstore, but this book can be found in its entirety on The Anarchist Library.