Step 1: Blade
The original striker that came with it was pathetic and blunt.
We replaced it with a blade given by a friend. I don't know what tool it came from, but his employers make expensive wooden furniture, and find it cheaper to replace slightly-blunt blades than to sharpen them.
Happily, the blade already had two holes drilled in it, presumably for attaching to the tool.
Step 2: Safety
Unfortunately, the blade is, well, a blade. Being sharp all the way along, every strike drew blood.
Not a useful feature, but easily solved by adding a whole 5g sachet of Sugru as a safe grip.
The whole job took less than five minutes, but the fire-starter is now easily ten times more effective than it was.