A friend and I stayed here for a 5 day stop in Madrid and we absolutely loved it! The apartment was very close to Plaza del Sol, and was within walking distance of many of the city's main tourist attractions, as well as lots of fun shops, restaurants, and bars, and we felt safe exploring the area at all hours of the night. We were also close to a metro stop that allowed us to take convenient day trips outside the city.
Sometimes the neighbors were a bit loud (music and a dog, and some construction downstairs), but this was only during daytime hours and the only reason we noticed was when we were taking a siesta in the AC.
Sergio was very helpful when we arrived and followed up to make sure everything was going well. We would definitely stay here again!