The workload isn't small, but yes, how well you do in it depends on how much you understand and how well you like it.
I like extension better because it offers me more freedom, its by far more intellectually challenging than the AOS or modules and because it really did change the way I think about things. I think that really does get reflected in the way you write.
Oh, and you learn to compress a lot of info into a short amount of words. Condensation, condensation, condensation.
I did Romanticism this year, and extension was one of my favourite subjects. Some people in my class hate it though.
You can always drop it. Give it a try, its a fantastic course!