You will find that the small screwdriver blade on the side of the tool will allow you more control when tightening the cock screw w/o buggering up the slot. The length of the tool gives much more leverage to turn the cock screw tight- whether the flint in wrapped in leather or lead.
I Used to carry all kinds of tools in the bottom of my possibles bag, to take care of problems in the field. The Flinter's tool has allowed me to leave most of them in my range box in the car, or camp.
You don't know me from Adam, but if this was just some gadget, I would have gotten rid of it long ago, and I would not recommend it here! A lot of thought went into this tool. I have tested it for making sparks, but carry my flint, tinder, and striker in a separate Tedd Cash "Tobacco " Tin. I bought those items before the Flinter's tool, so I continue to use them.
I knapp my gun flints in the lock, using a raised frizzen so that the flint strikes the heel of the frizzen, to remove a spall from the bottom side of the edge, and leave a clean, even, sharp new edge across the with of the frizzen.