What is a flex pen? It's a fountain pen with a flexible nib, which is designed to give you as much variation in line as a dip pen. Noodler's is especially famous for coming up with an affordable version that is also adjustable.
Here is the pen:
I will draw a veil over the slight struggle I had with the adjustable feed and piston-fill mechanism, and move on to how it writes (and draws!):
|(No, I can't write in Elvish, why do you ask?)|
|Noodler's Heart of Darkness ink in Daler-Rowney cartridge journal,|
Winsor & Newton artist's pan watercolours.
I'm very pleased with it. It looked a bit cheap in the seller's pictures but feels nice and solid in the hand. There is a strange smell at first, which the Fountain Pen Network says is normal for resin pens from India, but I'm not too bothered.
It's quite tricky to use right out of the box though (look it up on the forums for instructions on how to adjust it to your own style), but for me it's a small price to pay for a fountain pen that draws like a Mitchell copperplate nib!