Also not really suited for Plex, since the transcode performance would be awful.

Right, the IO perf has been bad.

But IMHO, no one should be running a NAS without ECC at this point. It's on the "my RAID doesn't scrub the disks" level; it's just begging for silent disk corruption that propagates its way through backups and is impossible to fix with software solutions.

Depends so much what's on the NAS.