angel4us Prague #2 has both nitrates and nitrites in it whereas sure cure has nitrites but no nitrates in it. The addition of nitrates makes it a better choice for slow or cold curing where as Sure Cure or #1 cure is what you use for things you are going to smoke with heat like snack sticks. Unless you are cold curing something then use Sure Cure.
Adding more cure isn’t going to give you more shelf life. FSIS/USDA regulates the amount of ingoing nitrite into a sausage, and the maximum allowed is 156 ppm, so you would not want to go above this. Our formulations are designed to be within the limits as regulated by the USDA.
Let us know if you need anything else!