Actually it's quite a shame for the Gitlab team that they don't offer a similar official CLI. The gitlab software is high quality in general, and obviously it's doable by a third party to implement such a tool.

There is also the extra helpful hub: https://github.com/github/hub

It is a wrapper around git (you can alias it to the git command) that adds GH-aware things, like checking out a PR by URL or number, or opening up the repo page with `git browse`.