I have a little different take. I cut my gunsmithing teeth on standard, internal 1911 extractors. They are relatively easy to tune, and if made of good, properly tempered steel, they last and last. However, they MUST be of good steel to hold up, and if someone tinkers with the spring balance on the gun and accidentally converts it from controlled-round feed to snap-over, even the best extractors will break. The external extractor does not have to have such an exact temper, since it pivots on a pin, rather than being its own spring. As long as it is heat treated to sufficient hardness and is not too brittle, there is more latitude in metallurgy to be forgiven. Also, it is less susceptible to damage from snap-over feeding.
I've had to fix extractor problems on more guns with external extractors than internal ones, proportionately, although I've not worked on as many external extractor 1911s as those with the original design. The externals are maddening to work on, at least for me, and I've typically found myself replacing a bad one, never being quite sure what was wrong with the original. My friend 18DAI has had good luck with the Smith design; I've worked on both Smiths and Kimbers with external extractors that puked. He's right about the original Kimber design, but they have tweaked it on some later models, and they seem to work well. The new Kimber extractor looks much like the one on Glocks, and Glocks don't have many extractor problems.
Said all that to say this: An external extractor on a 1911 is a solution to a nonexistent problem, but they aren't all bad. I still prefer JMB's original, and while I own LOTS of 1911-types, I own none with external extractors. Doesn't mean I won't, I just don't.
