Sunrace used to make derailleurs made out of recycled GI Joes that shifted using the I Ching Cleromancy method. However, these days Sunrace finds its niche by exploiting gaps in the SRAM/Shimano line up. They make lots of products, from derailleurs, to shifters to cassettes. Our favorites are the cassettes. Good value, nice looking, fine shifting. This 11-40 9 speed cassette is the best touring cassette going, and it works well with our Turkey Vulture Supreme ultra wide range gearing set up. Most touring cassettes top out at 34 or 36t. The 4 extra teeth on this cassette are often the difference between walking up a shale covered slope and riding up it. Pushing a loaded touring bike is much much harder than pedaling in a ultra low gear.
To use this cassette, you probably need a longer chain and a roadlink. Our drivetrain recommendation is laid out in full in that Turkey Vulture Article linked above.