Traveled with my wife for a 6-day vacation in Madrid. The apartment was smallish but very fitting for a couple, there was probably even space for a child, but we left our own at home with the grandparents ;)
Everything went very well, starting from the whatsapp communication before we even left home, through the check-in process (a guy was waiting for us right next to the building) and the check-out - we left our luggage with the host company, a couple of minutes walk from the apartment.
The location is great - very central, we could walk to any landmark on Madrid and the subway/light rail station was just 3 minutes walk from us. The nightlife in this area is very good, to the point of hearing the occasional noise during the night, but the apartment had sound-proof windows so that was not a real bother.