I have used Keybase since it first showed up on HN for Comms and Git. Technically I have done the proofs for identity, but no one cares about that.

The Git usage was really nice. It's fast and secure. While I didn't use it for most projects (because I want them on github/gitlab for various reasons), it was very useful for backing up machine specific configs and history (using a script and mackup). Knowing that it was well encrypted made me not worry about what was being backed up, if there were credentials, etc.

As for comms, I used the 1:1 chat with a friend for quite a while. While it worked, it's slow. Sending messages is a little slow, sending images is VERY slow. Anytime the app is closed (like constantly on the phone), re-open times were slow (for decryption). Eventually I gave it up and moved those few chats over to Telegram (Because it's secure enough for most conversations).