Non-toxic is typically used for waterfowl. And .410 generally isn't going to get the job done for waterfowl. I imagine that is why very little of it is made, why it is so expensive, and why shot size selection is so limited.

The volume of shot in the shell, or the actual quantity of pellets should actually be the same, but it is using a shot material considerably less dense than lead. Which is why the amount of shot weighs less.