Our stay in Madrid was amazing, a lot thanks to the great location of this apartment. The place is modern and clean, and had everything we needed. As for the sleeping situation, there is a big opening between the bedroom and the livingroom where the couch is. As we were four friends traveling together it wasn't a problem, but I can imagine that can be a different matter if you travel as two couples.
The hosts are available over messages. The offered taxi deal for late check in was much needed after a long day if traveling. The wifi works for normal use, but we wanted to relax at home with a movie one of the nights, and the streaming was kind of slow. We couldn't connect it to the chromecast but had to watch it on my laptop instead. Not a big problem though.
From the apartment you can walk to a lot of great spots, we didn't even use the metro at all.