I've got an Agfa Isolette. Good features: internal hinged mask for 4.5X6 and 6X6, very compact - my wife calls it my point and shoot. Viewfinder is good and adjusts for the two formats. It falls down relative to your requirements in that it has no rangefinder. Also some flare from the uncoated 1936 optics (and some holes in the bellows). Use it a lot though because it is so easy to carry in your pocket and still get interesting images.
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Took this on a recent visit to the Palomar Observatory. The dome of the 200" Hale telescope.