That "pill box" derailleur, and a similar design from Simplex were nice derailleurs, who's only serious drawback was that the cage would get loose from the shaft. When it did so it would rotate down and jam onto chainring teeth. OTOH it was otherwise a reliable unit that was very accommodating of various chainring combinations. I always liked that the cage could be adjusted to match the curve of just about any chainrings, unlike modern FDs.
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