Using without an account
you can run your own controller and dont have to have an account
I needed to run sudo to use the zerotier-cli, I suspect I could change the permissions of the authentication token files but either way this was a blocker until I figured this out.
I'd like to work out the best way to handle permissions for this issue and include it in the wiki if that suits whoever is maintaining this page.
Zero Tier interface did not appear until reboot
When setting up the zerotier-cli for the first time, I couldn't ping my friend's computer. Although the zerotierone daemon status showed no errors there was no interface under ifconfig.
After reboot, the problem was resolved. It'd be good to have this as a check to avoid others running into the frustration of having a correctly configured network but left unable to ping because of this simple oversight!