I sharpened a 12 penny nail and have been using it to engrave aluminum flashing. A 10" x 10' roll of it is only $8. It's easily cut into to 8"x10" pieces by just scoring a few times with a utility knife and t-square and bending back and forth until it snaps clean.
I use maximum pressure, multicut 4 to engrave all the lines in the metal, then optionally etch the metal.
This is working quite well, but I plan to upgrade the tip to a sharpened tungsten TIG electrode for even better "bite" on the metal.
EDIT 3/11: The sharpened tungsten didn't work out, I was unable to find a way to actually get a fine enough point on the tungsten, so it wouldn't scratch well in all directions..
Instead I bought a hardened steel pre-sharpened scribing tool that I cut in half to fit inside the machine, and have mounted it in the pen holder but not actually tried it yet.