I (also a lifetime Plex Pass user) decided to try it out ~6 months ago, and I've switched over. I haven't had any gaps in functionality yet, though YMMV of course. While it isn't better than Plex (which is still fine for now), it isn't worse either, and I trust the Jellyfin devs a lot more than the Plex devs at this point.
I must be old school. I never got on board with Plex, because my "lifetime" licenses for PlayOn, TVersity and Twonky all ended up completely useless. Yes, those licenses still work, but you can't get the latest versions which provide support for the latest codecs, features, etc. There's a cutoff on the versions that "lifetime" license allows you to upgrade to, and some of those licenses were not that cheap at the time.
So of course, Plex is going to engage in the fuckery that they are. JellyFin on the other hand, for the amount it costs is surprisingly low on janky behavior.
I switched to jellyfin about 6 months ago and I can say it is definitely worse. I’m constantly fighting to fix thumbnails, fix episodes to be in the same show, force rescans to get it to even recognize a show that already exists. I never had any of these problems with plex. Plex also defaults to transcoding which fixes a lot of gaps with clients that don’t support certain codecs. I’m often running into issues where infuse can’t play DTS so I need to reencode before I can play the movies.
Also in the process of ditching plex I switched to audiobookshelf for my audiobooks and I have to say it’s also crap. It’s constantly refusing to start playing, or pausing for a really long time before playing.
All that being said I’m not switching back. It’s been a pain but it was worth it.