I wouldn't say "prone." Although cylindrical, Pencil 1 is weighted on one side to help prevent that from occurring. Clever design.
Clever design is the five sided graphite pencil with attached rubber eraser I used to use when I was 5yrs old. Not at all prone to rolling around on a slightly inclined surface, intuitive use of an eraser opposite the pointy end and no need for over engineered weights to keep it stable. Double-tapping to get an erase function in the new pencil is a waste and a missed opportunity. Hopefully the next iteration will finesse the design to be more intuitive.