I have been thinking about honesty and radical honesty the past couple of days. I haven't read the book, although I have poked around on the website. I recommend looking at the FAQ page. My other information about it comes from Tristan Taormino's Opening Up (pages 42-45), which admittedly is a biased perspective as Tristan isn't a big fan of the practice.
After looking through the website, though, and reflecting on Tristan's take on it, I don't think I am a fan of radical honesty. Honesty, yes. Radical honesty, no. What is the difference?
To me, honesty is about being open with my feelings with myself and the people in my life. It means being clear about my intentions, motivations, desires, and needs. It means owning my feelings. It means owning my mistakes and making a commitment to doing better, as best I can. It means asking questions. It means answering questions. It means keeping the lines of communication open as much as possible. It also means taking other people's feelings into consideration, and framing your honest communication in ways that take other people into account. It means recognizing that what I say has an impact on others. While I can't be responsible for how others react and feel about my communication, I can understand that what I say and how I say it has real consequences for the listener.
Radical honesty, from my limited understanding, is about being honest at the expense of anyone else's feelings. My feelings and ideas and opinions become the most important thing when practicing radical honesty. I understand the need to be honest in order to alleviate discomfort around something that you previously were being dishonest about. I think being in tune with your mind and body is really important. I know that if I feel guilty (feeling like my behavior and ideals of myself are in discordance) or uncomfortable with something, I have a serious need to disclose whatever it is I am keeping in. Being honest can be a serious release, and build trust. However, I think this also needs to be balanced with kindness, compassion, and consideration. Spouting off simply to release your own feelings is not appropriate in my mind. I also definitely understand the value in not maintaining a persona simply because you are scared to be your real self. I think the Radical Honesty take on this aspect, on being an authentic and real person, is a valuable one.
I really do think that context is important. I think that the people and personalities involved are important. I think that keeping kindness and compassion as core elements of honesty and communication is key. I am also really unsure that radical honesty is the way to build relationships in a healthy and sustainable way.