0.5 is pushing it, but for normal size writing 0.38 is a sweet spot of fine for most people. I use a 0.3, and I immediately notice bad paper because it becomes somewhat scratchy. This is in gel pens.
Looking at jet pens, yours seems to be a marker pen, which generally needs to be thinner so it won't bleed. Similar to how ball points need to be fat (0.7mm is called fine) to write smoothly and make a dark enough line.
Looking at jet pens, yours seems to be a marker pen, which generally needs to be thinner so it won't bleed. Similar to how ball points need to be fat (0.7mm is called fine) to write smoothly and make a dark enough line.