In the days before integrated brake/shift levers were the norm, there was little alternative to the traditional downtube shift levers. If you wanted to keep your hands on the bars whilst shifting the only option was bar-end levers. Having started riding road bikes with downtube shifters, I fully appreciate the usefulness of having both hands on the bars, particularly when shifting around corners or on descents.
Bar-end levers essentially feature the same mechanism as downtube levers except they are mounted inside the ends of handlebars. The mechanism in these shifters features a miniature ratchet which evens out the lever movement from shifting down (against the derailleur spring) to shifting up (with the derailleur spring). This is called a retrofriction shifter, made famous by Simplex.
Jackyll as piloting a tandem is difficult enough without having to worry about shifting downtube levers.
I've used plenty of bar end shifters before, however the light feel of these and the ratcheting action make these some of the best for friction shifting. Now they are back together again and ready to go on the bike. Thanks for reading!