Hmmm the two most different i have are one from FYGT which i beive may have come from the group buy on here, and a woodlore bouggt one which I think is a fireflash branded one? the thinner group buy one is very much softer and give no where near the amount of hot sparks that the fireflash one does which is much harder and thicker, the ones from the blast match are imo the same hardness bottom the fireflash ones, the both give consistent sparks where as the group buy softer one gives a good shower only if scraped hard down a longer length( this could well be due to the width though) but all start fires very well
I've taken this from sharkdesigns:
Why Have Two Types of PyroFlint™?
Standard PyroFlints™ are generally a little easier to generate sparks from, due to the higher percentage of pyrophoric alloys in the mix at manufacture. The sparks generated are a little cooler than those produced from the higher Iron Durable PyroFlints™ and do not live as long, but you get quite a lot more of them and they are easier to produce. Durable PyroFlints™ are a little harder to generate sparks from than lower Standard Iron type, due to the slightly lower levels of the pyrophoric alloys incorporated into the mix when manufactured. However, whilst the Durables produce less sparks for the same given effort, than the Standard ferrocerium rods, the sparks that are produced are substantially hotter and have a much longer lifespan, which enables them to ignite a wider variety of tinder types within a greater degree of ambient humidity levels and degrees of tinder dampness. In addition, Durable ferrocerium rods are much more resistant to corrosion, hence their name, than the Low-Iron Standard ferrocerium rods, plus you can scrape off a quantity of Durable ferrocerium rod shavings that can then be used to ignite even damp tinder, which is virtually impossible to do with a Standard ferrocerium rod.