I was fairly weak in Spesh last year, so the dot point notes and simple steps quite helped me. But as it is like, 2 minutes a page, you cannot get a full in-depth understanding, or atleast a studrdy grasp of what they say. Despite the 5-6 mins breaks that they gave, it is difficult to concentrate(for me, imo) for 3 hours, especially on new concepts....I did the summer school.
However, if you are going to do a mid-year lecture (I assume they revise Unit 3 content? Not sure of they head into Unit 4...I think they are the Winter School lectures

) you would already know everything (to a decent extent) of what they are going to cover and so it would just be reinforcing. Go to it if you want, but I find revision completely boring, and I would rather go through my reference material and do maybe 20 extra practise exams.