I have stayed at Gregory's place for three months while completing an internship, and he is very respectful and outgoing. I really enjoyed my stay. Location wise, you are pretty close to the Bart station (10 minutes walking to Balboa Park station) and to the bus stop off Mission. To save money, I just walked to work every morning and evening even though it was an hour away. That being said, I walked in the dark, and have not had anything stolen. Sure, I got some cat calls, but nothing serious or life-threatening. The streets in Mission can get somewhat sketchy at night, but the neighborhood where Gregory lives is very safe and comfortable throughout the day and night. If you have pepper spray, good common sense, and a white belt in karate, you should be fine.
Food wise, you are close to Safeway (10 minute walk) and Whole Foods (20 minute walk). Trader Joes is a bit far (a short bus ride or an hour walk).
WiFi works pretty well, but if you need to download large files, it was difficult for me to do so on Gregory's WiFi. I had to go to a coffee shop for that specific incident. However, I would say that I got my homework/work done just fine in the evenings with his WiFi.
Have a nice stay!