All of my communication was with Natalia, who was managing the listing, and Randi, who met me at the apartment. Natalia was responsive, and accommodating. They were changing the locks when I arrived, but Randi allowed me to drop my things, change quickly, and even met me later on in the afternoon to give me the new keys. He was available via WhatsApp for the duration of my stay, and was very friendly and helpful.
The apartment is in an unbeatable location, in the heart of Malasana, with cafes and shoppes in all directions. I felt very safe in the neighborhood at all times of day. As others mentioned, the apartment is very small, with very tiny windows, and is therefore quite dark. The back of the building location meant it was very quiet, which was ideal for sleeping/siestas. However, I wouldn't necessarily want to spend too much time hanging out in the apartment, as there is no view/balcony, etc...
My only real complaint is on the size of the bathroom. I understand that a lot of European bathrooms are small, and often everything gets wet during a shower - no problem. However, there was no drain in the non-shower part of the floor (the shower was elevated a couple of inches), which led to puddles of standing water that never fully dried during the course of my stay. I would have appreciated seeing photos of the bathroom before booking, so I could make a more informed decision.
That being said, it was an overall very pleasant stay, and is perfect for 1-2 people!