I think I like traditional flint and steel (F&S) better. Both fire piston (FP) and F&S use charcloth or could use tinder fungus if you can find it in your area. F&S is more rugged. Despite my breaking my striker due to foolishness, I was able to still make it spark. F&S is not all that dependent on the flint part. With a little effort you can find many types of rocks that will through a spark with your steel. You might even be able to get your knife to replace the steel for sparking. So as I see it, it is a pretty versatile system.
With the fire piston, you become pretty dependent on the mechanical functioning of your unit, the same way as you would a lighter. Those o-rings might just fail on you from sitting there over time. The fire piston works or it doesn't work. With F&S you have options...Look for a better rock or something.
The one advantage I might see is the FP might require a bit less fine motor control which could be useful in some situations. However, I'll side with Bushman5's critique here. You find yourself in trouble, its unlikely you are going to go to F&S or FP to make your fire unless that is all you have. Of course, as somebody mentioned, why would that be the only thing you have on your body....If you are smart enough to have primitive fire methods at your disposal, you could stick in a little ferro rod in there somewhere?
Do I want a FP? Hell yeah! I also want one of them rope lighters that Storl sells. I love fire! However, I'm a bit like others on here who think of them as a bit of a party trick. Of course bow drill is also a party trick. But you get all the girls with the bowdrill
