Chose them for a client due to built-in CI (as opposed to Github), but the HTTP response time on the web UI makes it painful to use - I'm routinely seeing ~1s response times on pull requests and CI pipelines, not to mention that the provided CI "runners" seem overloaded and your jobs often stay in a pending stage for several minutes (can be solved by running your own instance of gitlab-runner on an AWS box).

Personally I'm moving that project to Bitbucket - they now have CI pipelines too.