The forum may well have auto-generated SASS styles, but I'm referring to the website which has hundreds of classes with names like "border-0" which contain a single declaration, and markup that then mixes dozens of those classes.

"Active development" is also a way of saying "incomplete" and "subject to change". Too much weight/credit is given to stuff which is new and unproven.

I would figure the website would be equally as crappy as the forum is, which is my experience. Maybe it has so many extensions partly because they couldn't figure out how to make it work all in one go, or just lack imagination. I think " incomplete" is pretty accurate.

One other thing, I thought that maybe another attraction was that Flarum also hosted for free, which would appeal to someone who wants a forum at no cost, but they do not.

I not interested in beta testing anything new and unproven, I'd be looking for: how long has it been around, what's under the hood, and is it still supported/in development. Is it overbuilt? Does it try to do too many things? Then I would look at user forums and see what kind of problems people are having with it. Then I might install it to a virtual machine for a test spin and look at the code.