I have a couple of them.
They work great. It's been so long since I bought it, can't remember who I got it from.
Private e-mail me. I will sell you the extra one.
Cut the tip off with linesman pliers and file smooth. Then file a flat spot about 3/16" long and about 1/4 or so of the nails width deep and your done. I tap the nail head with a knife or my leatherman tool. Works like a charm and it's fast and foolproof.
I'm not a flinter, but I nap flint for other things. One of the most controllable nappers around is the point of a deer horn. Really fine for small dressing moves.