Ranked in these QuestionsQuestion Ranking
Pro Free and open source
All of GitLab CI's code is open source and under the MIT license.
Pro Parallel builds lessen test times
Tests are parallelized across multiple machines in order to reduce test times considerably.
Pro Highly scalable
The tests of GitLab CI run parallel to each other and are distributed on different machines. Developers can add as many machines as they want or need, making GitLab CI highly scalable to the development team's needs.
Pro Quick setup for projects hosted on GitLab
Since it uses the GitLab API for setting up hooks, the setup of GitLab CI for projects hosted on GitLab can be done in one click.
Con Officially only integrates with GitLab
Gitlab CI can only be integrated with Gitlab out of the box. In order to use it with another service (like GitHub or Bitbucket) with which you are hosting your repository, you have to use a third party service to make this possible. This adds additional cost and maintenence overhead.
Con No parametrised or on-demand jobs
You cannot use GitLab CI to build on-demand jobs with or without parameters.