Phabricator is a very good tool! But calling it a substitute for GitHub seems a bit off. GitHub (and GitLab) revolve around repositories. As the name implies they are focused on git and git workflows. As a user you are using `git` most of the time when interacting with the systems.

Phabricator on the other can supports `git`, but that's just one of the supported storage systems for phabricator. As a user you are using `arc`, phabricators command line tool.

I've seen many people having issues with using `arc`, having used, say github, prior to that. This got better recently when the `arc land` workflow was improved.