For those unfamiliar with FreeBSD, this is using base OS tools to manually create this type of immutable jail/container. This can be done with 'less effort' by using a jail manager.
Author of the article seem to know what they are doing so I'm puzzled why they don't use `bsdinstall jail /path/to/jail` to implement basejail instead of manually unpacking archives.
No need for separate custom rc script to start `lo1`, it can be done with `cloned_interfaces` directive in rc.conf.
Updating and upgrading jails by passing `-b /path/to/jail` to `freebsd-update` works, but new recommended way has lately been `-j <jailname>`.
Cool article overall, the beauty of FreeBSD is also in possibility to do things in many different ways.