I think a lot of people are giving less credit to this idea than it deserves. The .410 is far from non-lethal, and the weight/size of the shells would alow for larger magazing capacity. That is all that matters for a self defense weapon right? In additon, it has less recoil, always a bonus for accuracy and usability, especially if a smaller member of the household needs to use it.
Claiming that the user of a gun should become more accurate instead of getting a bigger magazine goes against most self-defense philosophies. Yes, accuracy is important, but in an emergency situation, you want as few reloads as possible.