My home NAS is also exposed to the internet.

    up 298 days, 20:42,  1 user,  load average: 0.00, 0.01, 0.05

"zgrep ssh auth.log* | grep -i failed" has no traces of any intrusion attempts whatsoever, just me not being able to type.

The distinction is, though, that the SSHd on that box is running on a non-standard port (220)... so that certainly makes a difference.