I know Git inside and out, but I had to use Mercurial for a client a couple years ago. I found it to be the most baffling and nonsensical source control experience of my life. It might be a case of cross-contamination. Like you said, each SCM uses similar terms for different concepts, so my Git knowledge may have unfairly colored how I expected similar terms to work in Mercurial.

But stuff like: "hg log" gives you _every commit in the repo_?? When is that ever useful? How do I get only the commits that lead to the current state of the repo? Mercurial doesn't have branches; instead you're supposed to _copy the whole directory_[1] at the filesystem level?? Of course this is ridiculous, so they invented "bookmarks" which are actually Git branches. The extensions thing you mention is also a ridiculous chore. Just have sane defaults. I also found hg's output very dense and hard to understand and read, poorly suited for human consumption.

I dunno. I'm sure Mercurial is fine, many people use it every day, and likely my strong Git bias was affecting my ability to learn Mercurial. But I found it far easier to just clone into Git, use Git to do source control, and then export back to Mercurial when I'm ready to share my work.

[1] https://www.mercurial-scm.org/wiki/TutorialMerge