Carbolin 19 helps the body preserve and build mass even when dieting. Indigo-3G works as a nutrient partitioner, sort of telling the body how to best use carbs for fuel instead of letting them turn into body fat.
You could definitely use them together if your goal was to drop fat and build muscle. Using one other the other would depend on your exact goal and your current condition, also your diet and training a little bit.
With Indigo 3G, you don’t need/want to go super-low carb because it needs carbs in the diet to do its job effectively.
Carbolin 19 can be taken on empty stomach or with food. That shouldn’t affect the results any major way. Just be sure to take two separate daily doses, as suggested on the label.