I’ve been using the Plex DVR for a while now and it works just fine (except that it crashes when I select German teletext as “subtitles”. Not that I need it, but it definitely shouldn’t crash playback). There is only one thing I miss from my previous cable receiver, and that is skipping the pre-recording time.
It’s actually quite simple: the receiver starts recording a few minutes earlier, but automatically skips this time when starting playback until the original start time of the program. From that point you can then fast forward and rewind to find the correct start. I’m not sure if it uses some embedded metadata of the stream to find out the actual starting time, but most programs seem to start at the right time, with the exception of some TV shows.
To me, this sounds like a good (and simple) addition to Plex with all the new skip features (ads, intro) in mind.