It's the default on recent Synology NAS, in my experience. No particular issue in my limited experience. Mostly transparent for the user.
My rough understanding is synology did some pretty heavy modifications to btrfs in their implementation though... (a quick google finds me nothing to back this up, but i remember reading about it somewhere...)
I'd like to see them move to full disk encryption rather then their current approach.
For RAID5, they are using it on top of LVM, but with some modification - the synology implementation hooks LVM and btrfs together, so it gets ZFS-like properties.
There's a guy on the internet, who was playing around with it: https://daltondur.st/syno_btrfs_1/