[amai]

Old Mac Book Pros are very silent and could be used as good NAS. Unfortunately Apple doesn't support modern versions of Mac OS for them, and also doesn't offer any security patches. So the hardware is still quite capable, but the software is too unsecure and unstable to really recommend old Macs as NAS.

[fragmede]

Depends on the person administering the machine. Linux is an option that can run a recent version with security updates.