My Old Timer is similar, has a small slightly curved blade in addition to the three you have opened. I'm actually comforted knowing that I'm not the only one whose Old Timer blades have rusted. Mine are a bit worse. But that main blade can be made extremely sharp and it holds the edge reasonably well.
Spyderco Delica in my left pocket, Spyderco paramilitary 2 in my right.
I'd LIKE to buy a ZT0560, but I don't have the money.