Well, I'm in the process of finishing all my notes for unit 3, which will be updated ferociously as I go through completing practice exams, whilst also completing practical exercises.
Unit 3 is a massive overlap of units 1 and 2, and if you have a firm understanding (not just a cram for the exam type understanding) of the practical components of units 1 and 2 you can easily finish off this unit thoroughly during these holidays. The exam really doesn't cover that much content, obviously due to the fact that it is only testing one unit of knowledge.
I'm planning on being able to complete the exam by the end of these holidays, if not this week. Especially due to the massive load of important SACs coming up during this term.
So in short, I think it is an advantage, any extra work is an advantage over the next kid.