I have three Titanium Duopars on bikes, one is on a tandem. I vote it the best shifting widerange derailleur ever made. I agree with what has been said about fragility, however. You should never pedal backwards, or roll a bike backwards when equipped with Duopar. We stopped selling them for that reason (although the mechanics kept special ordering them for their own bikes). They are also a terrible derailleur for mountain bikes.
There is more difference between the steel and titanium Duopars than just the material. The steel version is all riveted together, and the many joints loosen up much more quickly than the titanium version. The ti has pins with circlips holding the body together, and can be almost completely disassembled. It's just looks a lot better made.
Of course, I use to disassemble my Huret Allvit to clean it and grease the pivots. Later I learned the correct method was to either dunk it in carb cleaner and spray it with oil, or throw it away and replace it with something else.
Steve Barner, Bolton, Vermont
Anyway, what's the story with the Huret Duopar? I know there were three versions, alloy and titanium, all alloy, and alloy and steel. What are peoples opinions on these versions shifting, merits, and quality? Also what's the current market for these things these days?