1- no brand makes brifters, or just gear only controls, that are meant to link together to allow more then one control location. The cable movement needs for shifting is different then that for brakes. Now one could daisy chain some and find out easily enough and report back here. (Excepting the previously mentioned electronic controls)


2- The lever rotates a cylinder which the cable is wrapped around. Some sort of rotational position holding device (ratchet teeth and pawl or G spring/ball and detent/"index gear") to trap the cylinder at a point that the cable has moved only enough to make the der move enough for one shift. The unit has advance and release functions which "undo" the holding device allowing further shifting in either direction when the holding device re engages. there are many on line images of the internal workings if one were to do some searching.


?- This, and other, forum has dozens of threads about the malfunctioning of every type of shifter control. The more complicated the control is the more likely of more types of problems, from wear, incident, poor maintenance or manufacturing issues. So I would say that brifters have more to go wrong. Given the number of friction levers I see that are falling apart from not being kept tight, that have worn/broken bits, that are broken from impacts I am unable to say any one design is more idiot proof. Andy.