Overall very good and highly recommended!
Clean, Central but quiet location and kind hosts.
We had a very good time at Guillermo & Alfonso's apartment!
They were kind to order a taxi in advance for us when we arrived in Madrid. The place was clean and tidy, and Guillermo was waiting for us for a brief and warm welcome.
It was a very nice surprise to find ourselves in such a central location that is also VERY quiet. It was only on two occasions that we had to take a metro and the rest of time we walked Everywhere on foot over the course of a week.
Communication with Guillermo & Alfonso was easy and good even though we had a pretty good idea on where we wanted to go around the city so we didn't ask our hosts for recommendations.
We had an evening flight back home, and since the place wasn't booked for the following day, they let us stay with our luggage in the place until the time we had to leave for NO extra fee - which is a Really nice thing to do !