stay in 2 unit and study your ass off like there's no tomorrow! there's honestly no point in general. Its really the same amount of work just they give you a formula sheet in the exam + it's more solving questions that have problem solving 4 - 5 lines of text long + multiple choice. 2 unit maths has shorter questions, however requires more skill or "independent knowledge" as their is no formula sheet. TBH the first section of 2unit maths (year 11 content) looks like fairly easy stuff. It's only 20% of yr 11 stuff in 2 unit and 30% yr 11 stuff for gen. so i don't think you would be fond of grabbing a yr 11 and 12 maths gen books and still studying your ass off. so you may as well just stay 2 unit and study hard.
PS: why do people call it 2 unit? both maths courses are 2 unit. It's mathematics or general mathematics.