I've never had any success getting paper to light from a spark unless I've been able to make a fuzz. Some materials don't fuzz well - eg paper money is quite poor in my experience. It's certainly a good idea to carry known-good tinder rather than relying on improvising with what you find in the field.

I don't think much of the magnesium as tinder, though. The wind blows the scrapings away, or I knock it when I am trying to scrap, or something. It takes time and effort to make the scrapings, which I wouldn't want to try with cold hands.

And I found I didn't always get stuff to burn with it. For example, I once made a proud little pile of magnesium scrapings on a hex fuel tablet, and managed to get a spark to it without knocking it over - and it burned hot for a few seconds but not long enough to light the hex. All the heat went up instead of down (damn that physics). Maybe there is a way to do it, but it seemed to me I needed to use a secondary tinder - eg paper. Get the magnesium to light the paper, then use the paper to light the hex tab. So now I prefer TinderCard or the Sparklite tinder or cotton-wool based.