My sister's Mercier campus bike had one of these. I would say it shifted as well as the Simplex Prestige derailleurs that came on Peugeot UO-8s. But her Mercier was far prettier.

My Raleigh Super Course came equipped with the Svelto's ******* spawn, the Luxe. The Luxe was just a Svelto with a longer and more flexible cage. That mousetrap with red pulleys was so proficient at missing shifts and hitting the spokes that I had to upgrade to a Simplex Prestige. Eventually, Raleigh followed my example.