Unless you enable unPnP which is a security risk, you have to manually port forward or setup a remote server yourself. And unless you know what you're doing, you might open your network to potential hackers. Make sure to read up on reverse proxies or how to set up a vpn with Jellyfin.
Metadata for media files will automatically be updated by using media databases. This provides posters, movie trailers, descriptions, information about actors, etc.
More hardware requirements on Plex due to a useless/non-intuitive transcoder. When using lower spec hardware (eg SBC) Plex will not transcode or play HD+ videos. When compared to other packages (eg Jellyfin which transcodes nicely using FFMeg), Plex falls short on video playback and transcode settings to get videos to play (fastest/lightest option still fails).
Create a playlist and pre-cache all tracks on your mobile device.
It is also possible to update playlists and automatically keep the pre-cache in sync.
Active and lively support forums where the developers and other users engage to quickly resolve any issues you may experience, which will be few and far between anyway.
You can reach your media files on most smart TV's, some gaming consoles (PS3, PS4, XBOX360 and XBOX One), Android and iOS smartphones, Blue-ray players, DirecTV DVR, Roku and many more.
Some devices will support subtitle files by default, and for those that don't Serviio can hardcode them on the video while streaming. However, this increases CPU usage and will not work for low powered NAS devices.
If your wireless router is in another room, larger HD files can "stutter" a bit, especially when there are a lot of high-pitched sounds in the background.