It's a bit like with the compiler: it can be pretty and all, but ultimately I just want to write `make` and get my binary. When I need the details, I know where to find them.
a) basic Git isn't that complex b) Learning a dumbed down subset of Git won't help you long term
I would say that giving people a gentle introduction to stuff is great, but it's important to make sure that it is a launch-pad for really learning the tool properly in the future.
That being said, I think this will be useful for a lot of less-techy designers or copy-editors or QA people, etc. People who can just open stuff in Notepad because they don't need to craft code.
My rule of thumb for 'mission critical software' like version control systems - if you can't access its fully functionality at the shell when logged in to a remote machine then forget about it.
Gitbox is great for your workflow until the day you have to actually use git and you have no time to 'actually' learn git.
(Disclaimer: Tongue in cheek.)
I've had to teach plenty of people how to properly merge files using Git and no one has ever said "oh that makes sense". If a tool can hide the ugliness of merging conflicting files, even a little, it'll help a ton of people get used to using Git.