At the check in line the other day, an Air NZ staff member was walking through the queue promoting the twin seat to couples. Nice upselling, worked on the older couple behind me who I could hear discussing it afterwards.

Incidentally, I had a free seat next to me on the fairly full flight. Didn't use it for anything but liked the extra room and not having to fight for the middle arm rest, and my aisle neighbour stored his bag under the middle seat.