Mainly I am commenting on the rear derailleur. I've been around cycling for a while and still haven't seen a broken one. Fronts yes. In my opinion the prestige is a fine derailleur. I've had them on a couple UO-8's, and presently on a Super Course and the long cage version on my Grand Sport. They also are equipped with Simplex front derailleurs.

I stand by the Simplex Prestige and believe if maintained and adjusted properly will operate for a long period of time(40 plus yrs. and counting).
And that last sentence contains the key to why I think the Prestige has this myth attached to it, adjusted properly.
In the Boom years the number of bikes that were equipped with these derailleurs was staggering. Almost every entry level bike was equipped with these derailleurs. French, Italian, English, Belgian, you name it the Simplex Prestige was THE derailleur. And perhaps the shear quantity produced lead to the myth. By that I mean, if virtually every bike had them, then any derailleur failure was a Simplex. In my 40 years of cycling I have bent two Campy NR derailleurs. Is the Nouvo record derailleur faulty? No, its because for so many years thats the only derailleur I used.
And out of all those bikes equipped with Prestige derailleurs how many were maintained properly? How many were adjusted properly right out the doors of the local bike shop? In the Boom years the average bike shop employed mainly teenage kids. Building bikes that when shipped from France or wherever were a pile of parts in a box. These "mechanics" assembled bikes as fast as they could to meet the demand of the consumer. The lowly Simplex derailleur rarely was adjusted properly, rarely came back for the 30 day check up, and had a good chance of being shifted into the spokes of the rear wheel within its first summers use.
"I guess those Simplex Prestige derailleurs are junk". "They explode when you shift them". "They crack if you look at them".
All Fallacy!
If anything they were an inexpensive throwaway part, that when replaced, cyclists were finally informed of how to shift properly. And were given a new SunTour GT that was adjusted properly.