It is true that if you're looking for a finished, polished product, jj is very much not that. It's pre-1.0. Lots of things will change.

I still refuse to use anything else these days, but I can understand why someone else might not want to.

This was true of svn and git; both had command named the same as VCSs that were popular when they were introduced, but had semantics that were subtly (or not so subtly) different.

Unironically, it is. The underlying storage engine is git, which is rock-solid.

But to put it this way, I've been using jj for almost a year, and even without a 1.0 release, editor support, or mature tooling, it's still such an improvement over git, I've stopped using git 98% of the time.