In fact, GitLab 8.5, due the 22nd of this month, will heavily improve many views for mobile. This has been something we've been holding off on and we'll be slowing working more and more on it, as our UI matures.
GitLab 8.5 will have responsive views for most pages, but their functionality will be slightly limited compared to a full-browser, as we chose to hide certain elements (rather than a separate mobile view).
The mobile experience for github is not amazing either. It rearranges everything for no apparent reason and makes it harder or impossible to access what I want.
There's a lot of stuff going on in the sidebar and it took a while for me to figure out where things were. The mobile experience was also not amazing.
If you would like to take this conversation offline, I'd be happy to. I like Gitlab so far, although I'm only 5% in to my "migration" process.