I use fire pistons in Physics classes to give students an idea of the power of compression. To get a fire out of it you have to have a completely dry char cloth or similar tinder, good technique, etc. They are much harder to use than any of the more modern techniques. I would even consider it below a bow drill and similar primitive fire starting methods because you have to carry something to do it with. Those techniques can be improvised in the field. The space is much better spent on a mini Bic or matches. Even a ferro rod is much better. For an Altoids tin type kit, I use the metal Spark-Lite.

Respectfully,

Jerry