The reason I recommend it is because you can't rely on the CLI itself. Git commands can do weirdly counter-intuitive things depending on the version and settings of your git install. A command that works for one person may not work for another. Or worse, appear to work and fail silently. Or even worse, cause a problem that you won't find out about until later (if you can even determine the root cause at all).

That's why I recommended Fork.

Also, it's not $60, it essentially has an unlimited evaluation period (a la sublime text) so you can try it out for free for as long as you want, and pay if you want too (I have).

The linux port is in progress.

EDIT: just a sidenote, if you really want to force youself to go CLI only, you'll want to look into how git behaves differently depending on config. I recommend starting with this talk at NDC to get a good enough git config, then move onto Julia Evans blog as she's currently going on a public journey of untangling how the same commands can do different things in modern git.