By all means, use the derailleur. You might find it acceptable. I was just sharing my experience. And while technically the Huret is a knock-off, its quality is on par with the Simplex as I have seen the two side to side. Its design limits its functionality especially when compared the the Gran Sport from the same era. The paralleogram derailleur is here to stay. The coil spring is not. I have no idea what Hilary was smoking when he wrote that.