For Sale: Duell Bologna frameset, NOS

The right shifter has a little lever hidden at the back of it (1st pic). When you lift it the shifter engages in a lower step, shifting the chain onto the little plate fitted to frame (2nd pic). The idea is that with wheel removed the chain sits still tensioned.

I though they were very typical in touring/randonnees bicycle, don't think I've seen them on road bike before.