"I think using the edge from a hacksaw blade would use up the ferrocium quicker because of the teeth but I don't know if you would get better sparks. "
If you use the teeth of the hacksaw blade you get LOTS AND LOTS of sparks which does equate to faster usage of the ferrocium rod but is good to keep in mind when you NEED to start a fire and lost your lighter. The back side, the side without the teeth, or even better the edge of a broken hacksaw blade works great to. You do not need a carbonsteel knife to use a ferrocium rod, as when you use a true flint and steel is used it is the steel that is is being pealed off. Ues the best technology you got to do the job.
Cheers