You can unfold the cover, remove the cards, see the fronts, and it is only when you turn them over that you see the reverses are fully printed (in Russian) with details of what they show.  So, yes, they are unused; and no, you could not mail them as postcards in the usual way.  But they are the right size and shape, and deserve listing here anyway.  This set also marks the most different theme categories for any one entry, so there’s that.  Inside, a card of the National Library of the Republic of Tatarstan.  Grade: 1