Ubuntu Mate for the Raspberry Pi is coming along nicely. I am using beta 2 of the 64-bit version on a Raspberry Pi 4, and it works very well. However, I miss some of the utilities and features of Raspberry Pi OS. The raspi-config utility really, really needs to be included by default. It has a great many features and tweaks that you can't get any other way on Ubuntu Mate, such as overscan. Another feature that I miss is Overlay FS, which is nice if you have a slow SD card. Finally, I miss the SD card copying utility, as I use it all the time.
If someone could investigate porting these utilities and features over to Ubuntu Mate for Raspberry Pi, I would really appreciate it.