As a general rule, any derailleur system that worked well enough to be put into production probably worked well enough. If it didn't survive the test of time, it was probably because of some other feature, such as difficulty of setup, availablilty of spare parts, or that type of thing.

A notable exception to that rule: derailleurs with one pulley wheel., like the Campagnolo Sport. I've never tried one, but I understand they are pretty bad.

But two-pulley systems tend to work just fine, within design parameters. I had a bike with a Cyclo Standard derailleur for a short while. Date code on the Williams crank put the bike at 1934, which was consistent with the other components on the bike (Resilion brakes, Brampton free hub, early Marcel Berthet pedals, etc. It had a twist grip shifter on the handlebar. I didn't mess with it. It shifted perfectly, very smoothly, and very easily, and it feathered itself. That's an advantage of the old two-cable mechanisms (Cyclo, Nivex, Simplex 3-4-5, &c)-- since they don't have a spring to pull them one way, it takes very little effort to push them one way or the other-- if the shifter isn't feathered right, the friction on the chain is enough to move the derailleur, and the shifter, to the smoothest location (though it may take a while). The shortcoming of the Cyclo Standard was not that it didn't work well; it worked great. The problem was that it was a pain in the neck to set it up, a pain in the neck to change an innertube, and these are serious shortcomings.


I have a Trivelox Model B derailleur on one of my bikes. It's also from the mid-30's. It's awesomely primitive, and it shifts only three cogs. So pretty limited, but what it does, it does quite well.


These modern derailleurs that mount to a derailleur hanger integrated into the dropout, and that shift flawlessly over 11 or more cogs, are pretty cool. Take the shifter and matching derailleur out of their boxes, attach them to the bike, attach the cable (included) and make one or two small adjustments, and you're ready to ride/! That's way better than fiddling around with a Cyclo Standard until you get it just right, and 11 cogs are definitely an improvement over 3 cogs. So, sure, the new ones are better. But it's not because the old ones didn't work.