I think the .410 buckshot out of a handgun offers more potential wound tracts, which increases the amount of physical trauma you can cause with one trigger pull while greatly increasing the chance that your shot will hit something vital at close range.*
NG is right, I wouldn't want to use one in a situation where someone could open fire from across the street, or in a crowded setting, thus why I think Judge/Governor are niche weapons. But, if I knew it would be used under 15 feet, I would not doubt the power of 3-5 000-buck pellets. Even out of a 3" barrel, those will meet the 12" penetration requirement.
*Considering how few pistol shots in a firefight actually hit the heart, I'm saying that a good shot on COM has 3-5 potential wound tracts to hit the heart instead of 1.
With all that said, you have to look at more than just the round, but also the platform...
9mm and .45 are pretty close in "stopping power", with a slight edge to the .45, but overall the 9 has: smaller frame weapons, cheaper ammo, greater capacity, and less recoil.
*The .410 comes in a much larger package than your standard 9 or .45, and you will probably get a significantly higher amount of ammunition in the autoloader.
*In a situation where the BG is right on top of you, the .410 would offer a better wound tract.
*In an active shooter situation, the .410 would more likely hit bystanders than the BG.
*The .410 will have significantly greater recoil, especially if using loads with 4 or 5 000 pellets.
*The .410 ammunition is much more expensive.
Overall, I like the concept, but I just don't think it's the best way to go, the 2 biggest reasons are its size and its lack of long-distance accuracy. I pocket carry a 9mm and I carry a .40 on my hip, I'm happier with the faster follow-up shots than I would be with a .410 brick.