In 1965 Simplex upgraded their Prestige models, by replacing the thumb-wheel adjusters with adjusting screws. For some reason the Prestige Cadet only got one adjusting screw - the low gear one. All the other models (and also the 1962 Prestige Cadet) had both high and low gear adjusters.
This version of the Prestige Cadet is surprisingly well made and diminuitive. It has 35mm long parallelogram arms, whereas Simplex’s norm is 40-42mm. This suggests that it is not designed for 5 speed freewheels. At 127g including the hanger plate it is also, by some distance, the lightest derailleur in this collection.