But that would be publicly discoverable because of the new device name announced in your signature chain.
This first version supports basic text messages up to 4000 chars and attachments. What's preventing Keybase from adding a device for me, that's really just owned by Keybase or nefarious shadow organization X?
Key additions must be signed publicly into your signature chain , as determined by your signature chain. You'll see this policy in action when you install Keybase on a 2nd computer.
All of this is a requirement for performance and (upcoming) mobile notifications.
It's better than PGP because of many modern crypto best practices, easier and safer key management, and easier and safer identity lookups.
It'll make you either (a) type something on your first computer, or (b) enter a paper key.