Any new backup is hardlinked against previous in temporary 'in-progress' directory, then renamed to proper name at the end. If backup breaks, new 'saf backup' by default first removes 'in-progress' than starts things again (linking with latest good one) but you can 'saf backup --resume' to try to finish interrupted one. I prefer clean try again (which is the default) but --resume works well too.

> Can it automatically prune backups older than N days?

Yes, manually by 'saf prune' on top of 'saf backup' doing prune itself. Prune periods are defined in each .saf.conf, per backup source location, with the defaults of 2/30/60/730/3650 days, for all/daily/weekly/monthly/yearly backups. All defaults are easy to change per source.

> I don’t see anything about encryption.

saf doesn't deal with encryption, only with transport. I prefer to use other specialized tool for the encryption if I have such backup target that needs one.

Many prefer to deal with encryption separately, encrypting the volumes being backed up to rather than relying on the backup system to manage that.

Of course this adds a consideration to your system: how to backup your encryption keys, and use them to remount the volumes when needed, in a way that does not render the whole thing pointless by accidentally exposing your keys to the wild. Then again, the encryption included in many backup systems has these issues for you to resolve too.