The multiple device part seems tricky to improve on. I don't see how this approach can be tweaked to make it easy for non-technical people to access on multiple devices.

It seems like you have to define a new device on a existing logged in device before using the new device. Is there a way around that? If I want to log into an app for the first time at work and forgot to define a new device name at home where I already can log in, I wouldn't be able to do so from what I understand.