A lot of people have worried expressions when we told them that we were staying in the Tenderloin. But in reality, it's not as bad as people made it out to be. You just have to be aware and vigilant but we never felt unsafe. There are certainly areas that are best avoided but that's any where especially in a big city.
As for the apartment, it was quite cute and minimal, but enough for our needs. When we walked in, the radiator was leaking but after giving notice, management addressed it in a timely manner. As a heads up for future airbnbers, this is more like a furnished apartment rental vs staying at someone's house - so be prepared to buy bathroom necessities, salt/pepper/oil, etc. Also, if you are a light sleeper, it may be difficult - trash pickup days are incredibly loud from 6am, sirens, and sometimes random music / screaming at 1/2am. But that's city life lol.
Overall, the location was great, close to touristy stuff, good restaurants and bars, and transit. We would definitely stay here again. SF was a fun visit and look forward to next time.