Plex has a lot more polish. However, Plex also tries to shove stuff down your throat. If you want to share your meeting with friends, you need to have a Kodi pass or some bollocks. Jellyfin is 100% free.
Certainly it is not as polished though, but I managed to use it with my friend who are not very technically literate, and it works very well for them.
Every release improve the polish a little!
Edit: New media shows up for me pretty much straight away without having to do anything. Not sure what's happening there for you.
Edit: New media shows up for me pretty much straight away without having to do anything. Not sure what's happening there for you.