I purchased the Coughlan's Magnesium Fire Starter about a year ago, and finally got around to trying it out just recently.
At roughly $5, it seemed like a good deal: it had a flint for making sparks, magnesium you can shave off to get the fire roaring. Everything you need.
But it didnt.
The first glaring omission with this product is a lack of striking apparatus. Most flints will come wit a section of metal which resembles a small hacksaw blade. The purpose for this is to strike against the flint, which is what causes the shower of sparks.
Since there was no provided striker (and since I didn't want to make the long trek from my backyard into the house to find one), I resorted to using my folding knife.
The magnesium brick shaved off easily enough with a proper blade.
When I started striking, I learned you need to scrape off a coating before you will get any sparks. After about 10 fairly hard draws, I managed to create a fairly nice shower of sparks.
The directions state that you are supposed to direct the sparks at the magnesium shavings, which act as tinder. I found that the only way to actually get the magnesium to light, they had to be hair thin strands. By this point I was too frustrated to continue trying to create fire.
I could see where this product has it's uses in camping. But If you're wanting to start a fire without matches or lighter, I'd recommend you go for a product thats pure flint, like the Blast Match or Firesteel. Don't bother with the magnesium block, just gather some natural tinder of your own. It's more hassle than the effort is worth.