I prefer cgp, along with the specification. CGP does go along the specification but sometimes it’s not clearly in order, however it covers all the content in small, condensed note form which makes it easier to read, revise from and make revision resources from because it’s cut into smaller sections. It covers all the relevant content without using lengthy, flowery paragraphs, so personally it makes revising for me quicker and easier.
However along side I do use the specification to make sure I’m on the right track- like a tick list. This is just my option tho and others say different things- it really depends on learning style.