Peter, I've not had hands on experience with Btrfs at this point. Though I'd trust it on a NAS a bit more since NetGear already switched the ReadyNAS line over back in 2013. That at least added a larger group of "beta" users and likely led to a lot of improvements and some stability time. While the engineering group mostly changed, they still continued their general interaction with the rest of the community to help develop and improve the situation. It's similar to their past direct work on Netatalk which helped keep that project alive, while other NAS vendors of the era were simply taking code without contributing back.

At some point late this year I'll likely hack my older ReadyNAS unit to run the newer OS with Btrfs support to try. Doing so requires me to default the system and put data back on it, and I'm not quite prepared to do that currently. Though my personal goal is still to get to ZFS, and long term I'll be trying to hack the NAS to switch to FreeBSD to accomplish this. Or get a newer unit that is FreeNAS ready out of the box.

The core advantage of ZFS and Btrfs is still better data integrity then any other filesystem can offer, since it can check the data and not just filesystem metadata at any time. The rise of IO speeds and compute power has helped enable this without the drastic performance hits such required back on some proprietary SANs I worked with a decade or so ago.