I don't know what they teach in bridging exactly - but it's essentially the bits of a 3u course that are relevant. Personally, I don't see why you can't self-teach the parts that are relevant yourselves.
However, that requires you to be pro-active and actually find the time to be committed to it. I have a friend who goes to me for maths help. He wants to take MATH1131 but he only did General - so he's self teaching himself the 2u course, taking a 3u bridging course, and coming to me with help with the 4u course and other stuff he doesn't get. That's what works for him, find what works out for yourselves.
First year uni maths is a good chunk high school revision to make sure the NSW kids, the interstate-transferers and the international students all are on the same page and learn the same thing. And then after first year, then you go on to more specialist stuff.
So for instance, if you did 4u - then great, that's the sort of preparation you need for full advantage in first year maths. If you did 3u, you're missing out on complex numbers and a bit of integration. Also a certain mathematical maturity - which means the 'step' from high school to uni maths will be less.