The main advantages of Kopia, are speed and destination flexibility.

The off-site storage does not need to have Kopia installed. It can be a mounted network location, an FTP server. Whatever. A generic cloud storage bucket like Backblaze B2.

That’s why just a router with and external drive hooked up is able to suffice.

For all of these, you can connect multiple Kopia instances to that same destination, and each client can browse backups, restore from them, and backup their own files to the destination.

With borg, you need something like a Pi that can have borg installed. (You can also do this with Kopia, in which case the Kopia instance on the destination device is also able to manage the backups).

Kopia also beats borg and restic in speed. My daily backups typically complete within a minute or two. I used to use Duplicati, with which it was common for it to take up to an hour. When it started regularly taking more than an hour, I switched to Kopia.