GitLab CI integrates directly with GitLab CE installs, requiring no configuration from the end user. Compared to Jenkins, it will automatically link up with your repo and start builds on commits and pull requests. These are things you have to manually configure with something like Jenkins. As for Travis CI, the integration is just as seamless. GitLab CI talks to GitLab installs via the CE api and automatically pulls in your projects, sets the build status on your repos and assigns runners to perform your builds. The GitLab team has really done an amazing job building a CI offering that integrates really well with their CE repo app.