A firesteel is the same as a mag block but without the mag. (i.e. the striking surface of a mag block is a firesteel)
The problem is that the firesteel on the magblock is small and doesn't through as many sparks. Secondly, it takes a lot of work to get a significant amount of mag shaving to light, and when you do light it it only last for a second.
A lot of people, including myself, find it much easier to start a fire by carrying a larger firesteel, and different ignition material.
Some different ways of carrying tinder with your firesteel:
1) Make a fatwood block. Epoxy a piece of fatwood to your firesteel. Esentially it is identical to you mag block, but with fatwood instead of magnesium. (It is a lot easier to get shavings and dust off of fatwood than it is off of magnesium)
2) Carry Petroleum Jelly Cotton Balls. You can do this by making firestaws, stuff PJCB into a straw and seal both ends with pliers and a lighter, cut straw to desired length first. You can also put a cotton ball or two into a spy capsule. To make a PJCB smear the outside of the CB with PJ, when you want to light it, tear it open to expose dry cotton and set your spark to that. Lights easily and stays lit for a couple of minutes, not seconds.
3) Carry Char cloth.
Number two is my favorite tinder material, it is easy to make, albeit a little messy, lights easily, stays lit for a substantial amount of time, and is water proof. Try making a couple and use the firesteel on your magblock, you will fall in love.
Here is a great idea that I am planning on trying. It is a compact way of carrying a firesteel and tinder in one compact package. A PJCB and some fatwood shavings would be some great fool proof tinder to store in these.
http://www.bladeforums.com/forums/showthread.php?t=512075
sroll down to post #8.
Also, many people don't carry tinder because they are able to make fine enough wood shavings that will catch a spark:
http://video.google.com.au/videoplay?docid=-1618781026416227624
the only problem is if all you have is wet would it will be harder than if you have your own dry tinder.