When I was younger, I was an active cyclist who put thousands of miles annually on my 10 speed racing bike. I used 3 in 1 oil on my chain. 3 in 1 was designed for bicycle in 1895. It is still an excellent chain lube. That said, for my Radcity 5 plus step through, I use Muc Off dry lube. It is wax baed, does not attract dirt. 21st century bike have come a long way since 1895.
I believe 3 in 1 was invented to keep from soiling a rider's pants like motor oil. I wonder if low film strength was a big tradeoff. You push hard on the pedal to pull the chain around the rear sprocket, and that force is concentrated on a very small contact area between pins and rails.
I rode thousands of miles on English bikes with 3-speed hubs. A chain guard kept my pants clean, and a front fender that ended five inches from the road helped protect the chain from grit. I'd remove the chain, soak it in solvent, and soak it in motor oil. In retrospect, I think the higher film strength of 30-weight motor oil gave me better lubrication.
Rad bikes don't have chain guards. To keep my pants clean, I tried Finish Line teflon lube 19 months ago. The first application was disappointing. It was expensive because most of what flooded the chain ended up on the ground. It didn't keep my pants clean and, as others had warned, I soon needed to apply more.
I began applying it with a 20-gauge needle on a 1oz polyethylene squeeze bottle, putting one drop on each side of each pin and watching it wick in. I could do a chain with 2.4 grams or about 3ml, meaning that a 240 ml bottle would lube a chain 80 times.
If you apply it directly from the black bottle, you can't see if it has been shaken enough for the heptane to dissolve all the teflon. I think that's why many say it doesn't last. If you squirt some into a squeeze bottle, you can squirt it back into the black bottle if it doesn't look milky; with enough teflon dissolved, it's viscous enough that it will look milky from the tiny air bubbles that remain for a minute or so after shaking. Another clue is to squirt a drop on a finger. Like 5 w motor oil, it should feel more viscous than 3 in 1.
Teflon has an affinity for iron. If I lube the pins and the next day spray the chain with water, beading will show that the teflon has spread over all the metal surfaces. As long as I don't wipe the chain before the heptane evaporates, this protection will last indefinitely as will the lubrication. It's smoother and quieter than I thought a chain could be. I give the credit to teflon's high film strength.