It’s still missing the send and receive features from btrfs. And while they say it’s more stable than btrfs, it’s yet to prove itself (through widespread use), and is marked as experimental in the kernel config.

I recall snapshots not being quite as cheap as on ZFS.

Probably somewhere between kernel 6.8 and Fedora making it default (that’s broad I know). I’m guessing around kernel 7.

Until you start seeing its reviews. Or else, you should try using it for data you can afford to lose (unimportant or backed up) - which is what reviewers would be doing anyway.