I just installed it a few days ago, so I just have preliminary opinions.

The dark theme is OK - probably good on battery, but this is always plugged in. Dunno if it's good for eyes too much older than mine though (e.g. the white text on black background for the menu bar seems less crisp).

I almost exclusively use Chrome on this. One thing I have noticed is that refreshing on B-J doesn't always seem to "take" (e.g. the number of comments doesn't always update correctly), but I don't know if that's something about Mojave or something about FYPW on B-J (it's going to be updated soon and maybe some tinkering is going on behind the scenes).

Otherwise, I don't notice any issues. I haven't run any benchmarks or the like. It seems like just an incremental update to me - no speedups or slowdowns.

YMMV!! :-)

HTH. Good luck!

Cheers,
Scott.