I wouldn't rely on the Skycouch as a comfy sleeping option for 2 adults. If you're both short (under say 5"10) and of small build you'll probably get away with it OK, but if you're bigger you may find it uncomfortable.
In the handful of 77W flights I've had I'd suggest it's the perfect solution for kids, but not so great for adults. Economy on the 77W in regular seats is a truly horrible experience anyway with the 3-4-3 seating.
The Premium Economy offering is great but the Spaceseat in PE is a very polarising product. Probably 50% of people on here think it's fantastic and really good for sleeping, the other 50% think it's a terrible seat.