The cost the sky couch if brought is roughly inline with buying the three seats. Maybe some differences as there isn't the mass of a person and the baggage they carry. Plus no meal. And need less AC as less people releaseing body heat, so can run the engines at a lower thrust setting. That might not be much but for 12 hours it all adds up. It is basically getting people to pay for seats and never have people sit in them.

Also it gives you direct aisle access which disappeared from PE when the space seat went. No having to wake other people up or having them wake you up. Not having to interact with other people is a really nice feature, just can sit there, no one trying to talk to you or spilling over into your seat.

If its a couple it will be cheaper than two PE seats and you don't have to share with a stranger and get a bit more room as if sit by window and aisle and can angle legs into the middle if sleeping in seat.