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Yeah, I was referring to the "chisel" type. I'm not a professional tradesman, so this is only a guess, but I imagine the Greenlee knockout punches are best for high freqency jobbing that would wear out an expensive step drill very quickly. For most hobby work, a step drill is the way to go.
About step drills, I've heard that the two flute designs are superior to single for the reason that as they progress to larger and larger holes they remain perfectly centered. A single flute/edge step drill will end up ever so slightly off from the original center you started off from. Not a big deal for 80 percent of what you do, but sometimes really critical.
Knockout madrels still require a pilot hole, so it can't be argued that they're 100percent cleaner (less metal shavings) than step drills. A pair of step drills was another purchase some years back that proved to be brilliant.
Hole punches are really in a different league. Very thin metals, or rubber, fabric, paper, cardboard, etc. I've always made due with whatever was at hand before, with basically satisfactory results. But I never realized what labor savings, and what clean results were given by these things.
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one more for the quintessential workshop
