These are amazing ball point pens. The ink flow is very smooth for a ball (it feels like a gel, but won’t smear like a gel). The tips are strong, but will be rendered useless of dropped on the tip. They are of course refillable. Google them on the net. I think there is a Japanese supply store in San Francisco that retails them online. The hairline .25mm is great for quick underlays, .5mm and up for defining. The bleed is minimal with a fresh set of Copics or Chartpaks.
Pros: even flow, strong sketching nib, refillable, good detail work in the .25mm
Cons: $$, keep some refills nearby – the ink can move pretty quickly, lightweight plastic can feel cheap in hand