This is a great spot! It's a quiet room in a nice neighborhood. It is on a short street that connects a large shopping area with lots of cool boutiques and a smaller area that is mostly vintage clothing and cafes. If you are familiar with NYC, it reminds me of the border between SoHo and the West Village. It is really close to a metro station, so it is easy to get around Madrid and to and from the airport! So many great restaurants too.
The room itself if pretty simple, and very clean with good wifi. I could even do video chats with no problem for work. It is enough space for one person. There is a window that helps bring fresh air in.
As a solo (female) traveler, it felt very safe. I had absolutely no problems. The apartment is safe and there is an iron gate at the door. The neighborhood itself is also quite safe-- even late into the night, there are lots of people around taking part in the merriment of the area. It is well lit too.
Marlon is very kind and friendly and always willing to help. He was generous with his time and explaining things to me. Communication in English and my beginner-level Spanish was easy. I would return if I ever make it back to Madrid.