I’m a big fan of Kaweco, and I really like the Kaweco Sport.
The “classic” sport is made of ABS plastic, not glamorous but tough. It’s pocket sized and lozenge shaped:
Once you post them, they’re a decent size.
They come in lots of different colours and formats — I have a black “guilloche” with an EF nib, and a burgundy one with an ink roller tip.
The nibs are great. They also come in different materials like acrylic and aluminium and carbon fibre and now brass. The only downside is the section and nib are both short so you’re either going to hold the pen close to the tip, or hold it around the section threads. That’s actually more comfy with the cheapo plastic pen than the (much) pricer Aluminium, so for everyday use I’d go with the cheap ones. You can still get decent replacement nibs.
Cartridge only, though. I’m using the nice-but-boring Royal Blue that came with the pen, and a Visconti red cartridge (because I wanted the fancy Bakelite cartridge case).
Apparently the little coin on the case was for displaying a corporate logo when the cases were given out as gifts.