The mod could use a bit of extra explanation... I tried using this mod, but cannot tell any difference between it and vanilla assemblers. Am I doing something wrong?

@Author please change from using data.lua to data-final-fixes.lua otherwise the changes won't be applied to a lot of recipes.

And maybe change the contents of the file to:
STUFFING_MULTIPLIER = settings.startup["stuffing multiplier"].value

for _, recipe in pairs(data.raw.recipe) do
if recipe.normal then
recipe.normal.overload_multiplier = math.max(STUFFING_MULTIPLIER, recipe.normal.overload_multiplier or 1)
recipe.expensive.overload_multiplier = math.max(STUFFING_MULTIPLIER, recipe.expensive.overload_multiplier or 1)
else
recipe.overload_multiplier = math.max(STUFFING_MULTIPLIER, recipe.overload_multiplier or 1)
end
end

This mod makes assemblers craft until they're they're holding more than just a couple recipes' worth of products.