It is indeed independend and has a lot of nice ideas and theory contributions. It turned up after I stopped actively competing in computer Go, so I can't tell how strong it is. It certainly has a lot of potential and I'd probably pick it as a base to work from nowadays.
KataGo is also cool for those of us that use bots to review our human games because it has score estimator. With Leela a 0.5 win and a 20.5 win in the endgame can both amount to 99.5% chance of winning, but to us (amateur) humans that is not true.
There is a Go client that is distributed with Kata Go and was built for that purpose: https://github.com/sanderland/katrain and is distributed as a pip package, making it very frictionless to install.
With a tool like this, instead of waiting for a Go pro to visit our local Go club to review our kifu, I can have my game reviewed move by move until the end (not only the first n moves).
I can still have questions for pros, but they would be more specific.
Now, playing a superhuman intelligence bot can be unfun. Now matter how much effort you put in a move, you will just keep making your outcome worse with every move.
Another important use-case is that the AI can also tell you if a joseki is actually joseki, and how to refute a bad joseki move.