You can run both, since you have Plex paid for anyway. Then you get the best of both worlds, and can maybe get new users on the jellyfin. If they catch that last 10% difference or Plex goes to shit, and jellyfin is a platform you like since you’ll have low-stakes experience with it, maybe you’ll eventually want to move everyone over.
Plus if one service goes down the other may still be up which is nice.