The preferred seats are at exit doors. It only means you have extra leg room and won't have other passengers climbing over you when going to the bathroom. It is however next to the bulkhead where there may be parents with babies.
I have done preferred seating before on the A380 upper deck which isn't close to a bulkhead. It was worth it on a very long flight. I've done the Auckland flights more times than I can count but have never bothered with it but may consider it on the older 777-200ER that does SQ281.