I stayed at Valentina's place with my girlfriend for 5 nights while traveling to Santiago on vacation.
The place is perfectly located at Downtown Santiago, just 2 blocks away from the Santa Lucia subway station. Most of the points of interest in Downtown Santiago such as Casa de La Moneda, Plaza de Armas and Cerro Santa Lucia are within a 10-minutes walk.
While it's located at a very busy part of town, we felt like it was a safe neighborhood. Even at 11pm there were people walking in the street.
Santiago has a very comprehensive subway system, so it's a real benefit to be located so close to a station. Cerro San Cristobal, Costanera Center, Barrio Bellavista and other points of interest are a 10-minute subway ride away.
The building is new (according to Nelson, Valentina's father who greeted us upon our arrival, it's been built around 2015) and it felt secure.
The apartment is small, but very well equipped, with fridge, microwave, cooktop, hairdryer, washing machine, etc. Some reviews state that there's no air conditioning in the apartment, but during our stay the bedroom did have air conditioning (maybe it was recently installed?). The bed is large and comfortable. There's a couch but it's a small one; it may suit a children or a short adult, but I don't recommend it for tall people to sleep.
The WiFi at the apartment works fine, and there's a Smartv with Netflix in the bedroom.
Upon our arrival, Nelson gifted us with a bottle of Chilean wine, which was a very nice surprise. He also provided a BIP card (subway card) and a cellphone with a Chilean number (this was mostly used to communicate with him and Valentina through Whatsapp).
Overall, it was a wonderful stay and I definitely recommend this place.