I tried it and agree it's very buggy. If they can't get rid of the obvious bugs, how am I supposed to trust that my data is not exposed by much more subtle ones? I've un-registered and deleted my data.
I revoked address book access, deleted the conversations individually (I couldn't find a feature to delete them all), revoked access from Google Accounts, and removed the app from my phone.
I'm trying to remove my account too..