I spent a 3 nights/2 full days in this apartment during a visit to Madrid. The host was very kind and responsive, and they met me for check-in. I appreciated that they were flexible with the time for check in. Their apartment has a great location - it is a short walk to the heart of Madrid (Gran Vía, El Sol, Plaza Mayor, etc.), and public transit (metro or bus) stops are close, too.
The apartment was well equipped, but it had the feel of lodging that is there for tourists (and not a cozy Airbnb that someone lives in and has listed). This didn't bother me, but please do keep it in mind.
Lastly, I only have one complaint. The original listing said the apartment included a microwave, but I could not find one upon arriving. After speaking with the host, I learned this was their mistake, and they have updated the listing since. I appreciated the prompt response and resolution, but I was ultimately frustrated to not have a microwave to reheat leftover food!