The location of the apartment is in the middle of Madrid, so there's no need to take the Metro to reach the most popular attractions.
The apartment itself is very simply furnished and it looks very used in some places. Still, it's ok to stay for a few days.
Though, the communication with Mad4Rent was very disappointing. We had a problem with our key at the main entrance door of the building, so we couldn't get in (later, we were told that they had forgotten to tell us how to use the key correctly upon check-in, the key must be inserted and then slightly pulled out again). The first night, when we tried to get into the building and failed, we had to wait for other guests who were entering the building. We called and texted Mad4Rent, but we could not reach anybody. Considering it was already late that day, we tried to call and text them again the next morning. Nobody responded. Trying another number, they said they would bring over another key. As we wanted to explore Madrid, I asked when they would bring the key over. Then there was no answer until the evening, when I texted them again to ask about the key. Finally they replied and somebody came to get us another key. All this time there was no apology for these circumstances or an offer for a refund. This situation was very stressful for us, not knowing if we can enter the building when coming back to the apartment. In such an exceptional situation, I expect the host to react as soon as possible.