These are several dairy-based whey substitutes. All you need to make a buttermilk substitute in baking recipes is milk and white vinegar or lemon juice. I usually opt for whole or 2% milk and fresh lemon juice, but bottled milk will do as well. Buttermilk was originally the liquid that came from the butter-making process, but now most store-bought buttermilk contains lactic acid during processing.
These work in a hurry if you need buttermilk for a recipe and you don't have one handy, or if you have a recipe that requires a small amount of buttermilk and you don't want to buy an entire container.