Well, the only thing I would ever want to use for doing math is a mech pencil. It’s the only tolerable thing.

Although I occasionally use whatever I find laying around.

Well, I do use them, but the pens don’t hold up as well as the pilots. The coloring disintegrates and some parts fall off. They also feel low quality with the squeaky plastic.

EDIT: the g-2 refils are also slightly cheaper than the Pentel’s.

Yep. I used multiple for school since the third grade (I’m finishing highschool now). While the pen is great, the refils are terrible. They sometimes dry from sitting for ~2 months and become hard and scratchy (most of my multicolor ones are like this). But the Pentel EnerGel refils fit in the g2 (but not vice versa).