Well there are a number of ways of looking at it, but I think that a lot of the interest is from people who were used to using rangefinders in their film days, and frequently it's possible to have a camera with lens in one pocket, and another lens or two in another pocket. They don't always have to be that fast, just as compact as possible and as high quality as possible. Some days you might take the camera and just a 35mm or 50mm equivalent, other days you might want a 21mm equivalent and a 90mm equivalent as well. I frequently used to carry my Leica CL with 40mm f2 lens in one pocket, and a 15mm, 25mm and 90mm lens in others - all a lot easier to carry than an AF SLR with standard zoom. Would I have preferred a 24-120? Frankly, no, because there's something about using such a camera that imposes a simplicity of approach - real point and shooting, actually. It's hard to explain if you've not actually tried it for yourself. Oh, and incidentally it works just as well with a FED 2 as with a Leica.