I am just a beginner adult colouring book experimenter so I bought these pencils without doing any research. And I bought a book of "calming" illustrations to colour plus a Prismacolor pencil sharpener. Because the leads in the pencils broke in 2 mm chunks after a delicate sharpening on just about every pencil, instead of calming me down had me very frustrated. After wasting about a third of every pencil I decided to sharpen the pencils with a exacto knife which solved the problem.
If you are just starting out I suggest better quality pencils and a decent pencil sharpener. Or go for fine tipped markers. I did manage to complete one good masterpiece and notwithstanding the agony of pencil lead breakage I plan on continuing the hobby.