The pens are very fine - like any other fine-point roller ball pen. The highlighters are just like any other chisel-point highlighters. I got the highlighters because sometimes on a busy print, just darkening the fabric slightly with a light blue disappearing ink will work better to mark the fabric than a pencil or pen. I don't know if the highlighters work like that, yet.
I haven't tried all of mine yet, but I do know that they do disappear instantly when you press them with an iron. I read somewhere that they come back if you put them in the freezer, but I haven't tested that.