This is a pretty great idea. For what I often deal with, the GitHub desktop client is okay (though obviously tied to GitHub), but then I was sad to also realize they don't offer it on Linux. (Maybe they assume Linux nerds don't need GUIs?)

I tried Tower when it was in beta for Windows, but the cost is too steep to justify it for me. But it seemed to be a lot more full featured than the GitHub client which isn't good for more than basic commits. And again, no Linux there either.

I'd definitely go for a solid, open source git client, and it's obviously very relevant to GitLab's business.

Spend that money porting GitUp.co to multiple platforms instead. The only git GUI I've used that doesn't suck. Might be lacking in features though 8)