I tried setting up mu4e once. It wasn’t worth it. It took me literally a few hours of reading random blog posts to figure out the configuration, and that was only to download email. Never got around to setting up sending them, which is a totally separate process. Even then, there were lots of issues. First, it’s slow. Loading an email had a noticeable pause and was slower than GMail. Also, you can’t avoid HTML email…
I have been using mu4e for years, and am generally happy with it, and yet... I've never recommended it to anyone else. Unlike, say, org-mode or magit, which I'd happily evangelize. The pain points are what other commenters have said: - I don't find the default config a good fit for me, and run it heavily customized. As someone said everything in Emacs turns into a project... - Performance can be an issue, especially…
Also, the real test would have been my much more voluminous work email!
The HTML rendering isn't great, as you said, but you are two keystrokes from opening that email in a browser, if you have to.
And I have tweaked the config several times now, but I think that's mostly because I'm changing my (and the charity's) email, which involves a lot of shuffling about. Again, in six months, I'll have another look and decide whether it _really_ helped.