I picked up one of these Kaweco Sport fountain pens the other day...
I am unclear what is 'sport' about this pen, but it is a classic. The barrel is a bulbous octagonal design, something like a Rotring pencil that needs a diet. This shape feels wonderful in my hands. The plastic is lightweight and the nib puts down ink.
I bought a converter because I hate using cartridges, however the blue cart that came with the pen is just fine. I will prefer using this with Noodler's Ink however, I am an ink snob.
I tested a medium nib but was sent out the door of the shop with a fine. I will be swapping it, as the paper I am most enjoying these days really needs the broader nib. I do believe their fine is a fine and their medium a medium.
I still enjoying writing letters to folks I like and dropping them in the mail. I think it freaks people the fuck out.