The last tests are here: https://www.phoronix.com/scan.php?page=article&item=bcachefs-linux-2019&num=1
If you compare it with its rivals ZFS and bcachefs, in many cases Btrfs wins.
Consider that Btrfs does not enable any default compression, compared to ZFS which has LZ4 by default and from what I know in many cases it helps performance (correct me if I’m wrong).
You can also enable the “nocow” option for some folders, openSUSE does it on “/ var”:
This directory contains many variable files, including logs, temporary caches, third party products in /var/opt, and is the default location for many virtual machine images and databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and is created with Copy-On-Write disabled.
The main advantage over the classic file systems like ext4, xfs are the snapshots, it has saved me many times over bad updates, I only need one click and I restored my system. Many times I advance to the development version of Ubuntu, and I keep a snapshot of the stable version, if I need it it’s there, ready to restore it, and then go back to the development version again.
The zstd session helps you save a lot of space.