But in another post, you say that you are planning to add a second factor to Rublon, so that the user must enter a PIN when scanning the Rublon code. So it doesn't appear to be any more convenient that Google Authenticator, which is widely-supported, produced by someone I trust, and open source.

The idea of using QR codes for authentication is interesting, but I would be very careful in selling this as a highly-secure system that is capable of replacing two-factor auth.

To me, this appears no more secure than leaving a copy of your password in plain text on the phone - if someone gets access to your phone, they have access to all of your Rublon accounts. Compare this to Google Authenticator - in the same scenario, the attacker would still need to know my password as well as the token.