Got these for graduate school. I used them to highlight books rather than highlighters, and to take notes in class. They are a little weak (even though they are a .9mm lead) and break easily. I used standard .9mm mechanical pencils. They are also not strongly pigmented and turned out to be too weak for note taking. They worked okay at highlighting, I could read the text, and the highlights were not overwhelming or distracting. I could also write some small notes in the margins of my books, but you had to press hard to be able to read it later.
i was very disappointed how easily this lead breaks! i do not recommend it at all! i bought it to help stimulate my sons spelling lessons and make it more fun for him; it has added more heartache by breaking on almost every word he writes!