Ouch on burning your hand after the weld TomTomTom... That must have hurt.

The hinge in the Mu/Vigor/Vector is good. So is the one in the Visc D18, current Mariner and Vitesse models. One advantage to the Mu one is that when open the latch is not crossing it so the latch is perhaps less exposed to damage.

From a purely technical view the Mu version can be spoiled a little bit by misuse. The Latch needs to line up vertically yet it can spin and damage slightly the latch "catch" aspects of the frame that the latch engages. There is the ability to tighten the joint if needed.

On the Visc, from my view, the weakest part of the system is the connection bolt on the Latch pull. If there were to be a failure in this element it is an easy replacement. The bolt/screw can be adjusted to tigthen the bolt. Concievably it could be over tigthened to make the screw fail. I do not know if Torque settings are specified for this. Seems unlikely as the tension is only applied when the latch is closed.

The other aspect of the Visc hinge is that the current ones use 8mm Hinge pins. Older versions of the Visc in the P18 series actually had the Mu Hinge in them. Current versions of the Mariner and Vitesse (USA Models) also use this hinge and latch system and have 8mm Hinge Pins. I have found that older versions of the Vitesse used 7mm Hinge Pins. In my "split" system for putting bike halves into suitcases I found this 7mm complicated things. In the USA anyway, QR pins are only available in 6mm and 8mm diameters. I was able to adapt a 6mm pin using a 6mm/7mm bushing set. I did find however that smaller hinge pins are weaker pins and I did bend one accidentally
(T-handle and slow leveraged hinging).. It was not catastrophic, just made the Hinge not function as desired. My takeaway though was that 8mm hinge Pins are the size I want to have in my take a part systems and generally in the bikes. 7mm pins are nearly as strong as 8mm, but once down to 6mm the strength change can become significant.

This same issue leads me to think that Rack Bolts should move to 6mm from 5mm. We see the same process in Axle bolts moving, in some bikes, mountain and fat bikes specifically, from 10mm to 12mm.

I do have ways to reinforce a hinge, essentially locking it down, no matter what the hinge. I have not brought myself to making it but if I was setting off for Kazakhstan on a tour from Munich I might well do so.

All good. Thinking your welded Speed Pro will serve you well. When you get a new bike I'm betting it will serve you very well. Hang onto that Dual Drive. I just got a Dahon Anniversary Replica (30 speed) with the same (though mine is for sale rather than for me). Cool stuff.