The Premium Guide is designed to provide a list of all essential and important words related to a query. The Guide Premium allows you to know the right words to use, but leaves quite free as to the writing. You can write short texts as well as very long texts by following a Premium Guide.
The Oneshot Guide is designed to provide a canvas for writing about 300 words. You do not get the full list of important words for your article, but rather a sample that makes a 300 word text "ideal".
The Oneshot Guide is very framed, while the Premium Guide leaves more free the degree of optimization you want to freely apply.
The Premium Guide has the advantage of providing a nice overview of the vocabulary of your topic. That is, it can allow you to think of particular angles to use in your texts.