I ran into 5 problems:
1. It spit out vague error messages, requiring repeating the action in the CLI to see git's actual, specific problem.
2. There's no option to do the initial clone via ssh, which was a problem because http was failing to download the full repository.
3. It can't do merges, so you end up needing to use the git CLI anyways.
4. It crashed repeatedly while trying to handle large (1GB) repositories. Very sluggish and occasionally unresponsive on smaller repositories, too, especially with large single commits.
5. Various minor bugs. People would ask me stuff like 'how do I discard changes?' and I'd discover they'd gotten into a state where the menu would not appear until the software was restarted. They found it difficult to know when something confusing was inherent or a bug.
I wanted to love it, because it looks like it's good for beginners. Unfortunately, being pretty is not the same as being easy to use.
In the end, I introduced them to the git CLI, simply because I could always answer or find an answer to their questions about it.
I have since switched to SourceTree and it is working out well so far.
It's also mentioned in the blog post you've posted.
Disclaimer: I'm one of the developers of MahApps.Metro, I hope nobody minds the shameless self-promotion