/2 fork lock key blanks

I'm paranoid about losing a key and not having a replacement. So, first I called Bobs and got the price from them, then I visited my local hardware store, which I think is the best hardware store in the universe. The store owner tried several blanks and, voila, found one that fits perfectly. I'm sure any good key shop can get these blanks. He made me three new keys at 95 cents each.

You can get them from Bob's BMW at $11.00 each, or:
Go to your local locksmith and get an ilco key blank #vo6 for 95 cents

The BMW key blanks (Neiman, actually) are different from the Ilco blanks because they're made from steel.

I'm not sure why BMW keys are made of steel, it makes them difficult to have cut, as most locksmiths won't cut one unless they have a carbide cutter, which is unusual, or they don't know better. Also, it seems like the brass tumblers in the lock will wear out before the steel key does (though I've never worn either out).

How do they work?
I tried the same once and although the key went INTO the lock ok, it still didn't work even though I had it cut off my original, unused /5 key. At first we (the locksmith and I) thought he'd just not cut it right, he did another one really carefully, and it still didn't work. His best guess was that the critical key/tumbler mating area on the blank was thinner than a Neuman blank (it was, visibly) and that's what caused the problem.
I don't know the number of the other blank, no need to retain it as it didn't work, but it was a ILCO blank.