Unraid is also awesome for places with high energy cost: Unlike with your typical RAID / standard NAS, it allows you to spin down all drives that aren’t in active use at a relatively minor write speed performance penalty.
That’s pretty ideal for your typical Plex-server where most data is static.
I built a 10HDD + 2SSD Unraid Server that idles at well below 30W and I could have even lowered that further had I been more selective about certain hardware. In a medium to high energy cost country, Unraid’s license cost is compensated by energy savings within a year or two.
Mixing & matching older drives means even more savings.
Simple array extension, single or dual parity, powerful cache pool tools and easily the best plugin and docker app store make it just such a cool tool.
Unraid 6.12 and higher has full support for ZFS pools. You can even use ZFS in the Unraid Array itself - allowing you to use many, but not all, of ZFS extended features. Self healing isn’t one of those features, though, it would be incompatible with Unraid’s parity approach to data integrity.
I just changed my cache pool from BTRFS to ZFS with Raid 1 and encryption, it was a breeze.
I generally recommend TrueNAS for projects where speed and security are more important than anything else and Unraid where (hard- and software-)flexibility, power efficiency, ease of use and a very extensive and healthy ecosystem are more pressing concerns.