It's carved from a single block of wood, and I would guess that it was built sometime in the 1950s. It's signed "H. Duncan, St. Louis, Mo." And yeah, it works.
It wouldn't surprise me to learn one day that the first example of this or that type of electric mandolin was concocted not by the engineers working for the big-name instrument makers, but by hobby builders like H. Duncan. If only he'd bothered to put a date on the thing...