I want to check out that mischo-metal or whatnot, after reading its description -- which underscores that there are different alloy/mixes in the market for ferro-steel striking rods. I like how they sell various sizes.
I've tried a few and like those used in the Light My Fire units, which seem easy to generate sparks with for me, and for the youth in my Scout troop. I have also seen a few that are much harder to generate good spark with, including one this summer that a boy couldn't even get to spark at all and I had to really wrench on it to force a spark. Blah.
Now, those "classic" blocks of magnesium with a striker embedded in one edge? Double-blech! First, they're hard as heck to carve shavings off of without hauling around a file, and they're a great way to ruin the blade of a knife after you figure out the back of it ain't gonna do. Second, the shavings are more work than they're worth unless you do use a file and then the striker is only so-so. Don't do it at Scout camp, but the best use might be as a "beacon fire" when you're out in the desert with the big kids... think of it like a little bitty piece of a VW block. :)