My Channels DVR is out of service due to a disk problem. I installed a Plex server on my Synology NAS a few years ago, but have been using Channels instead. I just updated the Plex server to current release to see how its changed.
Only a few minutes of use but so far I'm impressed. The UI, including the Guide, seems fast and quite responsive. Same with FF, Pause, etc. It almost rivals my Tivos, which have the advantage of a direct connection by HDMI between the screen and the computer (no LAN involved). Of course the Plex UI is quite different from the Channels UI, so I have to climb the learning curve again. The Plex server found my HDHomeRun/antenna and gets live TV through it just as Channels does.
One thing I'm interested in is the reliability of the Plex client app. I've been using Firesticks on several TVs to run the Channels client and it has some problems. E.g., if you try to fast-forward before it's finished the previous click, often the app crashes and restarts.
I may also try out the new "Channels as a Plex Tuner" hack that was just announced.