Extension 1 Maths isn't hard to learn but the exams are quite difficult in some schools (like Sydney Girls sets easier papers while Sydney Boys sets harder papers). Having done Basic Algebra (absolute values, 3U inequalities, etc.), Functions (graphs, odd/even functions, domain & range, reciprocal graphs, etc) and Trigonometry at tutor so far, the exams have been quite hard and time consuming (I'm also a slower and careful worker so I usually just finish on time). Unlike 2U (where you can copy and paste your formulae), 3U really requires you to know how to approach questions. 2U and 3U content are easy to learn (to an extent) but applying your knowledge to the more difficult questions is quite challenging.
I mean the basics of Calculus (differentiation and even integration) for me was quite easy to learn by just reading Maths In Focus sheets which shows how the content can be learnt quite easily. Exams, however, will be challenging!