I haven't seen this discussed but even so it might bear repeating.

The Harbor Freight $3 magnesium fire starter blocks have magnesium that cannot be lit!

I saw a demo on You Tube last weekend and decided to test for myself.

I used a file to create very fine shavings off the block. I had a nice little pile the size of a quarter.

They could not be started with sparks either from the HF block or from the mil-spec Doan block I also have.

So to all intents and purposes, the alleged magnesium of the HF block is just a means of holding the firesteel.

I'll be swapping out the HF products in my get home bag immediately.

Also of note- using the mag block to actually get a fire going isn't as easy as one would think from the directions. I've been practicing this recently and it's almos more trouble than it's worth to scrape the magnesium flakes off the block. Other good tinder in your kit would be easier to use.