So I bought another ruler.
It’s a 20 cm aluminum one from Staedler.
I bought it while I was buying some other stuff because the cool one from Travelers Company is like 2-3 cm too short to let me draw lines in my Hobonichi in one go, so I just bought a larger one to use when I’m doing it at home. Which is most of the time.
It is far from as nice or cool as the first one. It kind of feels like the metal version of a plastic ruler. It is fine. Like nothing wrong with it. But it isn’t fun to hold or use. More convenient though.