Last I heard (~8 years ago), the RAID-like functionality in btrfs was very unstable and crash-prone. The impression I got was that there was not a lot of interest in fixing this. Then bcachefs came and ... appears to have gone nowhere AFAICT.

The non-RAID part of btrfs appears to be stable. It's the default filesystem on openSUSE and SLES. But I don't think it's ever going to reach feature parity with ZFS.

btrfs is suffering from a lot of old bad publicity and some poor design decisions around RAID.

But by now it is a great file system if you don't go near RAID5/6. btrfs has its flaws (ZFS has its own flaws!). However:

- It's used a lot, especially by facebook and Redhat (on fedora)

- Gets a lot of testing

- Sees a lot of bug fixes

- Has a lot of features

I haven't read btrfs code but given that it is a popular file system and Linux code quality tends to be good in popular subsystems I would hesitate to say its code quality is worse than ZFS in any way.