As far as I can find out so far, the rate is NZD150, which seems to equate to around USD110. As you point out, it's only going to be offered at check-in, and only to passengers in economy with an empty seat beside them, as it takes up 2 seats. This brings up a couple of points:
If it's only going to be offered at check-in, what happens when you have a load of passengers who don't have a reserved seat having to be allocated the seat next to someone who has already paid for the seat/bed? Will they give a refund?
I'd hope that the bed/seat will actually be standard in premium economy, but if not, what are they going to introduce to keep the distinction between Premium & straight Economy?