Hi Patrick,
I also have a Leicher chain handcuff in my collection I guess you know it . I got requests from other German collectors, who have identical chains with Leicher padlocks in the past. So IMHO this restraint is not extremely rare. I would estimate its value about EUR 30 to 40 (US$ 40 to 55) with original Leicher padlock plus key and good to very good condition.
My information about the restraint is almost not existent. I believe the chain being made by Clemen & Jung of Solingen, Germany, although a typical Clejuso Chain Handcuff look different (position of middle ring, no different chain link size). The padlock is made by the "Franz Leicher" Company of Munich, Germany. It is not impossible that they also made the chain. Unfortunately they never replied to my question. Leicher is still in business:
http://www.leicher.de/ - so maybe you try a request at this company, too?
Regards and happy new year,
Atame
http://www.atame.info/