I am often asked the question: does writing with a fountain pen improve your writing?
My answer is yes, although for me, there are a number of influences on how my writing ends up in terms of readability. This include whether I am sitting or standing. The quality of the paper and how the fountain pen nib flows across the paper, and the degree to which the ink will abosrb or feather.
But in terms of the general question, for me, writing with a fountain pen generally slows down getting the individual letters to words formed, and my writing is easier to read. I tend to write quickly with a ball point, but I also can write very quickly with a broad or smooth nib fountain pen. With the fountain pen, the nib is the major influence on how easy it is to read my writing.
So I gave myself a writing test, wrote with a ball point, then a fountain pen with three different nib variations. For each sample I was sitting at my desk. I tried to take no more or lerss care in writing then I do every day. I just started writing sentences with the first thoughts that came to me.
Scans of the writing are found below.
Writing with a ball point pen.
Montegrappa Espressione Ball Point, Medium.
Medium Nib, Fountain Pen
Delta 365, Medium Nib, Montblanc Violet ink
Broad Nib, Fountain Pen
Vicsonti Opera, Broad Nib, Waterman South Sea Blue Ink
Stub Nib, Fountain Pen
Stipula Etruria, Alter Ego, Stub 1.2, Iroshizuku, Yama-budo ink
Italics/Oblique, Fountain Pen
Aurora Tantelum, Italic Nib, Diamine Majestic Blue Ink
From my reading of articles on handwriting, it may be more how one holds the pen to form the letters that is an influence rather than a fountain pen versus a ball point pen. Generally, more relaxed writing flows from holding the pen in the hand, letting the fingers guide the hand and the pen across the paper. More tense writing results from holding the pen tightly between the fingers and then forming letters.
Age may also be a factor as I take it that those those than went to elementary school after 1960 learned how to write with more of a use your fingers to form the letters approach.
I think a fountain pen does help your writing because when you write with a fountain pen, people comment, if the comment includes "... looked great but I couldn't read it..." there is the feedback you need to slow down and work on your writing to make it legible.