The Magnesium Firestarter is a popular firestarting device. It is essentially a firesteel attached to a small magensium block and is typically a little less costly than a high quality firesteel. To use, simply shave off several small shavings of magnesium and use the firesteel as you otherwise would to ignite the magnesium shavings. The point being that the magnesium burns very hot for a few seconds and would be able to sustain a fire faster than a traditional firesteel alone, especially if the tinder is slightly damp.
Let me tell you that it’s not as easy as it seems. First you have the skill of learning how to properly strike and aim your firesteel. This takes some practice and a bit of luck. Eventually you will get the hang of it. Additionally, a little practice is needed to get a good amount of small sized magnesium shavings without overdoing it. Again, practice makes perfect. When you finally get the shavings lit, you will certainly notice a blaze of excitement for a few seconds then nothing if the fire hasn’t started. Try, try again.
In my opinion, it’s far more critical to have an appropriate dry tinder than to rely on the magnesium shavings to dry and ignite a damp piece of tinder in only a few seconds. Considering that a magnesium bar already has a firesteel attached to it then it can’t hurt to have the magnesium bar with you, however, I would rather purchase a good quality, larger firesteel than a simple magnesium bar for roughly the same price.
All in all, the magnesium bar is a descent, low-cost firestarting alternative but probably not the best choice if you can spend a bit more on a good quality firesteel such as the Sweedish Firesteel.