I agree the magnesium makes awesome tinder but for me, keeping space/weight consumption to an absolute minimum is essential. I do keep a very small magnesium starter in my car. The entire thing is actually smaller than that rod in the pic. However, I am looking for [a] rod(s) for practicing with the same unit(s) I commenly use for EDC which is/are quite small. Basically what I have recently been using for EDC is the rod from a Coghlan's magnesium starter with about .5"-.75" cut off the end and a small lanyard hole drilled into it.
Learn to improvise everything.