I recently flew twice in Oz using Jetstar to get to somewhere that no-one else flew to. The experience in Jetstar economy is that the seat has the tightest pitch (I am not exactly that tall or leggy) that I have ever encountered on any carrier, anywhere. Thankfully, the journey was only just over an hour so I was soon able to walk off the constrictions.
Other readers might wish to consider the alternatives (Virgin Oz and Qantas) should they have the option. Neither presented quite the same challenges in their economy cabins.
I honestly prefer Jetstar than Air Asia or Tiger Air but only use them for personal trips and want to save costs. Their routes are actually quite comprehensive, I heard they have one from Aus to Japan as well but never had a chance to try.