Pip,
Yup, it will also generate some AR sales. Enough to make any significant impact on the market? Dunno. Significant numbers of converts? Dunno, but I really doubt it. Again- could be wrong.
Unfortunately, just as in "our side", where there will be a certain number of previously undecided people motivated to decide the Black Guns may not be so evil after all, there will also be previously undecided people on "their side" (or previously neutral) who (whether they knew who Zumbo was before or not) will buy into the "Greatest Gunwriter In World Now Admits Black Guns Are Terrorist Weapons ONLY!!!!" statements made by the antis, without knowing or caring any more about Zumbo & his background, or the legitimate uses of said guns, than they did before. Today, headlines & sound bytes have much greater impact on those who don't have the interest, time, energy, or motivation to look into those pesky little details below the headlines & behind the sound bytes.
You're right, he was hardly a household word before. I'm moderately plugged into the industry, and I'd never heard of Zumbo till I saw him mentioned on the in-hotel TV channel in Vegas that constantly runs SHOT SHOW coverage during its run each year, about four years ago. Same Show, I stood behind him for a few minutes at the Remington booth waiting to talk to one of their reps. Otherwise, I've never read a word he's written prior to his career suicide, which I discovered on the gun forums. I don't read Outdoor Life. I'd safely bet he's much more widely known now than he was before.
Denis