At my work, we aren't using gitlab, but looked into it for our own hosted git and it's pretty nice, considering you can do properly managed repos. We do currently use phabricator though for source-code review, which is pretty nice. You can also introduce new code into the system through it using their arc tool. I think a mixture between gitlab & phabricator is pretty nice. Using phabricator for new feature buildout & gitlab for bug tracking would be the ultimate setup for me.