I have seen grooved frizzens on blunderbusses and other close defense weapons. I think that the first shot with a fresh flint would enjoy bigger, hotter sparks because the pressure the flint exerts per unit of area is greater. However,,,,,, after a shot or two the flint would have chipped back some and any advantage would be lost unless and until the flint was repositioned so that it, once again, concentrated the pressure on the ridges between the grooves. The bottom line would be a gun that would fire more surely on the first shot but eat flints ad a horrendous rate.
Best Regards,
JMC