Flew NZ J class for one leg (13 hours) and AC for second leg (14 hours) just last month. All window seats in J class on NZ were occupied but all centre row seats were available. The flight attendants made up all the centre row beds for window seat pax and so when we felt tired enough to sleep, we all crossed the aisle to sleep and then back to our original seats when we felt like sitting upright. It was a brilliant idea and worked for all of us. Lie flat seats were extremely comfortable and wider than AC seats. Mattress and down comforter were great!