Lived here for 3 months. Overall a good experience. A few pluses and minuses:
+ : The location of the apartment is amazing. Literally right at the center of the city. Walkable distance to grocery stores, movie theaters, shopping malls, and most importantly subway/BART and bus stations. As someone who didn't drive in SF, this apartment made it extremely easy to travel on public transportation. Walkable distance to Chinatown, Embarcadero, Japantown, and also Fisherman's wharf though a bit longer about 30 min.
Small but nice studio. The Airbnb provides everything you possibly need, from kitchen pots and pans to sheets and towels. Also has a vacuum, iron, etc. Pretty much you didn't have to bring anything and can live quite comfortably.
- : I didn't know that there is a homeless population diagonally across the street from the apartment until I arrived. Despite the apartment being kind of on borderline between Tenderloin and Union Square, I personally didn't have any bad encounters in the neighborhood, even when walking home at 9 or 10 pm.
However, the street noise can be annoying. The apartment is at a street cross-section, thus at day and especially night, you can hear motorcycles, cars playing loud music, and people yelling and arguing on the streets.
Additionally, I'm not sure if the floor upstairs is thin or something, but I can clearly hear people moving about/dragging chairs/throwing stuff on the floor. Quite annoying when you are trying very hard to fall asleep at night.
Overall, I spent one of my best summers here at SF and had an amazing time. Would recommend if you need a convenient location and are tolerable toward street noise.