Whether building a fire outdoors or starting one in your wood oven or fireplace, a fire starter makes it easy to get a small flame going. You can't just hold a lighter to a log and wait. To build a blaze, you need to start small, then add your larger pieces of wood until you have a large fire. The problem is getting that first spark isn't easy if you're working in windy or wet conditions. Matches and lighters are no match for these particular elements.
A wider ferro rod will often give a better shower of sparks and be easier to use, but there will be a weight penalty, and some users may find it awkward to hold. A dedicated striker attachment is good to have as it means you can use the ferro rod without requiring additional equipment.