I've been teaching myself pointed-pen calligraphy for 15 months. I now use vintage flex-nib fountain pens, but I started with G-nibs jerry-rigged into Jinhao X-450 pens, to break the heavy-handedness I'd acquired from a lifetime of ballpoint pens.
These G-nibs are XXF, with considerable flex. With no pressure, you get upstrokes that are hairline thin. With moderate pressure, you get downstrokes that are very broad. The extreme sharpness of the tip forces you to carefully control the pressure you apply. Any pressure on an upstroke will make the nib catch in the paper, spattering ink.
I still use G-nibs in straight pens and oblique pens, especially when trying new inks. They're quick & easy to clean, and their flexibility lets me test if the nib has enough cling to work in my flex-nib fountain pens.
