Prologue
So I upgraded to 13.0-RELEASE.
Upgrading from 12.2-RELEASE
The process
No new upgrade steps from the usual. Pretty uneventful unlike my upgrade 12.0-RELEASE which triggered an install error (details I cannot remember now). 12.1-RELEASE fixed it though.
There's a bug!
The Bhvye hosts upgraded fine. There's a known bug affecting my jails, where adding a vlan interface to a bridge returns Operation not supported
error. The workaround is manual, which means until 13.1-RELEASE is out I should avoid restarting the jail VMs.
Performance improvements
Despite articles touting significant improvements, it was largely unnoticeable for me; probably because none of my use cases demand high throughput. Moving on...
Conclusion
Unless you're looking to be on the cutting edge or need the network performance boost, best to wait for 13.1-RELEASE for a smoother ride.