Doing this for the last 7 years, too. One server at my parents, one at my home. Connected via IPSEC. I just migrated to ZFS on my offsite backup, too - this is just perfect with syncoid/sanoid atomatic backups and zfs-pull of dataset. Fine grained security but robust at the same time. It is the first time I feel reasonable safe regarding the "worst" that can happen.
We are about 120km apart, different electricity providers. If an area this size looses energy for a considerable time, data is probably my least problem.
If it's just two computers doing mutual backups, then having both stop temporarily due to a power outage isn't a big deal: All the data's still there, at rest, and being unable to access the backup server isn't a problem since you have nothing to make/send new data with anyway.
