Originally Posted by
T-Mar
They're not uncommon on French bicycles. Many manufacturers, such as Peugeot, with their large volume of domestic city bicycles, only brazed-on the shifter boss for the rear derailleur and retained this set-up on their 10 speeds for economy of manufacture. Consider this a conversion kit for adding a front derailleur. The large opening on the right side fits over the rear shifter boss, permitting both levers to be aligned.
IMO, due to their commoness, there is little value.
^^^
What he said, I see more Simplex setups like that but they're virtually the same as the Hurets in the OPs post.