One of my favorite features from GitLab is, without having to install any other tool, I can get a link from the response to create my MR. Such a simple feature, yet so convenient.
If you push a new branch to a GitLab project, we return a URL to immediately create a merge requests, which appears in the Git output in your terminal. So rather than going to GitLab, then clicking on a button, you just click the link in your shell.