It’s not good at letting you know when a disk is borked. And normally if you reboot a mirror with a bad disk, it will complain so you know to fix it even if you missed the log entries about it being down. Btrfs will quietly just let you boot into a potentially lethal situation for a mirror with a bad slave.
And there was something about scrubs that was janky as well
The issue last time I looked into btrfs mirrors was it’s poor reporting of disk problems and letting it boot with a borked drive. Might be fixed, but that was a 10 year old unresolved bug at that time. Seemed like a WONTFIX and I didn’t need that for a server OS drive.