The sandpaper needs an even surface to work properly. That could be hard to achieve in the field. I tried it on my PSK tin and some plastic cards as these are surfaces I´m likely to have with me. It worked but was no match to the real thing. When you fold the paper it tends to tear on the folding lines. Hence the size is very limited. As I was not really satisfied with it, I ditched it and went for a DMT folding sharpener. The additional bulk is well worth it IMHO.