This Falcon 20 is one of a legion of forgotten derailleurs produced in Taiwan in the last decades of the 20th century. Many are out on the road, working hard to this day. They are easy to find and very hard to find out about.
This particular model, also sometimes branded as a Falcon Dynamax 20, is a fairly faithful reproduction of a low-ish end Shimano model. Its one, non-Shimano, feature is the interesting, but rather clumsy, mechanism that adjusts tension at the b-pivot bolt.