I’m obviously not going to connect just one NAS to the UPS — that would be both unfair and unwise.

Well, look who’s here! My first UPS! Having lived on laptops for over a decade, I never felt the need for one — if the power goes out in the building, the ISP’s equipment will most likely go down too, and if it’s just a blown fuse, the router will reboot in a few minutes, no big deal.