TWSBI Eco with 1.1 mm stub nib. I picked this up recently because it’s reasonably priced and should be fine for ink testing. Mostly because it’s a demonstrator, and I can watch the ink slosh around. Cheap thrills.
This one has the 1.1 mm stub, which has nice line variation. The ink is a mixture of two green inks. Seeing the ink in the section? Sweet.