My experience is the same as CaptainGroovy's - it's a great, if thirsty, writer. I'm not sure if flex is supposed to be its thing because it's no more flexy than the Konrad. I didn't expect it to be - after all, that's not really a thing for a steel nib to do. But I must say that it's a joy to write with.
I filled mine with J. Herbin Stormy Gray.
It exist literary hundreds of different alloys of spring steel.
The main reason that gold was used for fountain pens traditionally is that gold is insanely resistant to corrosion it could handle being submerged in the old inks for a long time. when you use a dip pen you don't have that problem so you can use a non corrosion resistant steel.
Modern steel alloys can be both corrosion resistant and insanely flexible.
I am honestly surprised that manufacturer don't have a insanely flexible nib as standard.
If you do this with your Noodlers flex nib you get 4 mm flex without any problem.
If I wanted to manufacturer a nib that was insanely flexible I would use a alloy in the same family as the spring steel that is most commonly used in wind shield wiper.
Saying this I have yet to receive my Neponset but I hope that it is at least as flexible as my modified nib.
Edited by Agge, 10 November 2014 - 20:52.