Why don't I have a "users" setting? How to enable?
Wow, after a year of searching I finally have my own answer.

I don't know why, but my unit would never update from 4.2.2.  Any time I tried checking for an update, I would just get a "failed" message.

I found these instructions for manually updating to 4.4 (KitKat) and that worked as well as introduced the previously-missing Users menu!