Synology doesn't use BTRFS RAID but layers MDRAID (and some of their own code, I believe) underneath BTRFS, so they don't worry about the earlier BTRFS RAID issues. See:
https://www.synology.com/en-gl…ile_System_on_SynologyNAS
In my opinion, I would never run a NAS without a UPS, I don't care what filesystem you are using.
