This pen is one of those things that you don't need most of the time but when you need it you really do. It's handy when I have to sign credit card slips, fill out a form I didn't expect and anytime I don't feel like hunting for someone to borrow a pen from.
The pen's small enough and light enough that you don't notice it's there but telescopes into a long enough shape that it's not a pain to write with. I'm not saying that you'll want to write a dissertation with it but it's fine for a signature and note-taking.
The magnet that holds it in place is strong enough that you don't have to worry about it falling off. In fact, one of the coolest parts about this pen is that when you pull it out to use it the magnet holds it in place while it telescopes to full size. It doesn't bend or flex when you write and when you're done you just push it back into the holder.
The pen comes with three refills. Though refills are not sold separately on Amazon you can find them on the True Utility website or you can do what I do and cut ink stems from other pens to fit. You'll want to use ones that are mostly empty unless you're a fan of washing ink off your hands. It's also cheap enough that you can just buy another pen and more refills.