If you would like to reduce the calories and/or sugar, then you have a few options: You can use PB2 and sugar free maple syrup. I've actually tried it this way and they come out pretty darn tasty! If you use sugar free maple syrup, each bar only has around 5g of sugar.
Feel free to use your favorite nut butter in place of the almond butter.
Instead of pure maple syrup, you can use sugar free maple syrup, honey, or agave. Please note that honey is not vegan.
If you do not have access to puffed millet, then free free to substitute brown rice crisps, puffed rice, regular rice krispies, quinoa, or even chex. I found my puffed millet in the cereal section at Whole Foods.
If you are trying to make these vegan or gluten free, ensure that all of your ingredients fall into your respective dietary guidelines. For instance, make sure the dark chocolate is vegan.
You can sub any dried fruit you'd like. Also feel free to add a handful of chopped nuts, coconut, or more chocolate!