I've turned out several fire pistons from different materials on my lathe and conclude that they aren't reliable enough for 'survival'. Like Spock said, tender choice makes all the difference, and if you bring your own tender, you might as well bring matches. A match or lighter provides fire NOW, where fire pistons,bit and bow, fire plough,fire steels all require an extra tedious step to get actual flame. Try that when it's cold, wet and windy.
Fire pistons are fun to play with though. You basically have a single stroke diesel with one.