Definitely Svelto. Huret Allvit was a decent derailleur in it's day - however, it's day was 1962-65. Biggest advantage to the mechanism is that it was built to take a lot of abuse from riders who had no idea how to care for an adult bicycle. Which is why they were a natural for Schwinn.
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Syke
“No one in this world, so far as I know — and I have searched the records for years, and employed agents to help me — has ever lost money by underestimating the intelligence of the great masses of the plain people. Nor has anyone ever lost public office thereby.”
H.L. Mencken, (1926)