The word "these" assumes that the object pointed by it is know, or will be introduced immediately. Otherwise, it is just ambiguous.
If I say:
I did this.
I did most of these.
What will you understand? Probably not much, because there is no object to which "this / these" to point at.
This is why people usually say "most of these products" instead of "most of these".
You do not need to specify what "these" are if the objects and the other person are there with you and you can just point out to "these" with your finger:
What is the price of these?
You and the other person will know what it is about, but somebody listening to an audio recording will know the price, but will have no idea for which product.