The US bike boom fad was all about "10 Speed Racing Bikes". Anything with front and back derialleurs, a 5 speed freewheel and drop handlebars sold as fast as they could be assembled.
During those years Guiddonet style levers were primarily made by French brake manufacturers. They didn't appear on many bikes imported into the US except for a few French made mixtes and on a few special French touring models.
Most Guiddonet levers were not very well made. The better ones were made of metal. MAFAC made some with plastic levers and metal bodies. The plastic levers had a tendency to break especially as they got older making them unreliable and unsafe!
The 1st picture is a pair of cheap Guiddonet lever, maybe CLB. Next are MAFAC all metal levers. Last pics are the plastic lever MAFAC styles.
Guiddonet levers were designed for upright riding on drop bars. They were frequently used with randonneur style bars for touring, randonnée or brevet rides . They allow for effective braking with the riders hands on the sides or center of the bars.
Going back to the first premise about "10 Speed Racing Bikes", many if not most bike boom buyers would have been better served with upright bars because much of their riding was done with their hands on the top or center of the bars.
But... since it was a fad and few US buyers had much knowledge about riding 10 speed bikes with drop bars, Dia-Compe developed "Safety Extension Levers for their Weinmann knockoff levers.
They instantly became popular on new 10 Speed Bikes in the early 70's so much so that eventually Weinmann made an agreement with Dia-Compe to sell them.
The problem with those early style levers is that they were poorly designed.
The nylon bushings inside the Weinmann and Dia-Compe levers worer fast along with the bushing holes in the levers themselves and the nylon bushings on the special pivots used to mount the extension levers. The screws that held the levers on easily worked loose.
The attached pictures show the weak points in those extension levers that can allow them to jump out of the space between the the levers and the bodies.
My 1972 Gitane Gran Sport didn't come with "Safety Extension Levers". The shop was reluctant to install what they called "Suicide Levers" and explained why but I insisted. After a month or so of commuting the levers kept coming loose and popped out several times when I had to make emergency stops.
The other problem was the chrome steel rims with junk quality spokes never stayed true! Brakes need to be closely adjusted for Safety Levers to work properly (if ever). More than a few times during that month I went sailing through a stop sign when the levers squeezed all the way to the bars!
The shop removed them for FREE!
Something else with suicide levers was the tendency for inexperienced riders to do a header with tightly adjusted brakes. Newbies didn't know how to shift their weight back and tension their arms when coming to a quick stop.
MAFAC made some levers brake levers with well designed levers. I think that Shimano did too.
Don't confuse me with facts... my mind is made up!!!
verktyg
Chas.