They are a POS. An old POS, at that. 40 years ago, our soldering
instructor made it plain that he was forced to teach us how to use a
conductive soldering kit the military had purchased, touted as far
superior, especially for terminating cannon style connecors. POS. Any
skilled solderer can do it better and faster with a 25 or 50 watt iron
and a fine chisel tip, and any one who solders for a living will tell
the same tale.

Oh, they are also a pain, needing a ground connector as well as the
"hot" carbon tip. The only advantage was that in our kit, there was a
solder cup drilled into a carbon rod mounted on a bench top chassis
that was sort of OK for tinning lots of little wire ends, if you didn't
have a third hand to hold the wire, solder, and iron. Any hot solder
cup is good for that, it need not be a conductive solder rig. setting
the regular iron on the bench top and handing the wire and solder kind
of wiped out that advantage for tinning.

PS- you can use a "D" cell to do the same thing as the fancy "cold"
rigs they sell. It works almost as well as using a coat hanger, jumper
cables and a vehicle battery to weld.

Terry K