I love Frixion pens and use them every day when writing notes, and annotating drafts. They're also great for writing under a document camera when teaching. Alth

I love Frixion pens and use them every day when writing notes, and annotating drafts. They're also great for writing under a document camera when teaching. Although I wish there was an intermediate thickness between the thin ball-points and the really fat felt-tips. That said, I wouldn't use Frixion pens to write in books that I wasn't prepared to write in using normal pens. The ink doesn't completely disappear. The color also comes back (to some extent) if you put the paper in a freezer.