The UI is passable at best, but it has all the features I need and it works bugfree.
I tried merkuro before and while it is much prettier I had lots of strange issues and crashes with it.
But I recommend trying it out for yourself and seeing what works for you.
ps: before radicale, I had nextcloud on a rpi but after an automatic plugin update it died and I could not fix it. So I've replicated the features I need among alternatives: radicale, sftpgo, syncthing and navidrome.