I think the authors point was that if the NAS itself fails, with RAID1 you can hook a drive up to a computer and get the data. RAID5 hardware RAID will generall

I think the authors point was that if the NAS itself fails, with RAID1 you can hook a drive up to a computer and get the data. RAID5 hardware RAID will generally require the same controller for recovery, making the operation more difficult. ZFS or MDADM don’t have the same limitation, but there are other caveats there.