I bought these pens for quilting. I love that they can just be ironed off and disappear. (I realize they will reappear in freezing conditions, but they can just be ironed off again if the quilt ever freezes, plus, while I didn't test it, many people say they wash out.)
On light colored fabrics, they do exactly what I want.
On dark colored fabrics, they leave a white line behind. This means they are unuseable on darks. That is a huge bummer!
If you are using these pens for quilting, be very careful to test every fabric!
For writing: they write nicely, but not as smooth as a regular pilot pen. The erasing is easy, and only messed up one paper I tried it on, a greeting card, it rubbed up the background too. I'm not sure this is a great eraseable pen though, because you can't leave your work in the car (like many students do accidentally) as the heat will make it disappear, and if you do use the freezer to regenerate it, it regenerates the final work, and all previous versions- if you did a lot of erasing and rewriting, that could be a mess.
I did use it for "secret spy writing" to my nephew though :)