The apartment is clean and in a good location. You can reach the center of Madrid within 20 minutes walking and the area seems to be safe if you take reasonable care. However, we had a terrible experience with the host regarding the solution of a substantial issue that arose during our stay, which might also affect future guests.
The door lock of the apartment is outdated and not easy to handle. One night, we could not open the apartment with any of the two keys at all for multiple hours. We were 3 young men and tried many times to open the door. The host could not be reached.
After several hours had passed, at around 6:30 AM in the morning, I had tried again with all my efforts and it finally worked. However, weaker or elderly people would not have been able enter the apartment at all and would have been required to spontaneously book a hotel room or stay somewhere outside. We did the latter for a few hours. Thus, we acted in the best manner to keep the costs low. Booking a hotel room, which would have been necessary for the majority of potential guests, would have caused substantially higher costs. At around 6/7 PM in the evening, the door lock was serviced. However it was not replaced with a regular lock (the surrounding apartments were equipped with more modern locks and had the same old doors, therefore it should be possible to replace it).
We requested a reasonable compensation for that inconvenience, as we were basically unable to properly use the apartment that night / day (i.e. entering it within reasonable time and with reasonable efforts). Additionally, it should be considered that this is not a cheap offer and it seems unlikely that it is impossible to update the lock.
Nevertheless, the host seemed unwilling to provide us with a fair compensation and only refunded a partial 50% discount for this one night (excluding considering the various fees, that should actually be taken into account to determine the real price per night). We asked for a full refund for that specific night (by way of compromise excluding the fees), which seemed reasonable considering that it was not possible to enter the apartment in reasonable time and it was mere luck that we were able to enter it (in the early morning hours) at all. The host did not reply to our request for a more appropriate compensation.
Considering described circumstances, we assume that the hosts deliberately shied away from investments and the risk of such issue was taken consciously. It does not seem fair to pass on the deliberately accepted risk to the guests, which was the case however.