It still works very well. I'm using it on both Linux and Android. The UI is far better than its replacement inside uBO.

The uBO functionality isn't a legitimate replacement. I don't understand how that came to pass.

Those extensions are from the same author. I don't know the details but maybe gorhill didn't have the time to maintain uMatrix anymore and added the very minimum uMatrix functionality to uBO and settled for that. Luckily uMatrix keeps working.