I really like the fact that these Invisible Pens are so small and inconspicuous, yet are functional when making notes. They are the perfect complement to my Snap Flow notebook and, as such, ensure that I almost always have a pen available whenever I need one, even when I wasn’t expecting to need a pen. My Snap Flow goes everywhere with me and so does the Invisible Pen attached to it.
D1 ballpoint pen refills that fit the Invisible Pen are easy to find on Amazon (and other sources) and they are easy to replace. I’ve tested the process but have not needed to use a pen refill yet, so they last a reasonable period of time.