Stayed 2 nights at the green tortoise hostel and it was a good experience overall
First off; the security here is very very very good. so my sister and I felt very safe. The location is amazing; lots of bars, restaurants and public transportation so you will never run out of things to do. Place isn't that clean; but then again you're staying at a hostel and not a hotel. You need to share bathrooms which is the downside since one morning I had to wait 10 minutes until a bathroom got freed up because people were taking their time in the shower.
We shared a bedroom with 3 other girls and our room was on the main street so at night if you left your windows open; you hear a lot of outside noise (and since its beside bars; you will hear people late at night or even all night)
there's lock safes inside the bedroom too which was nice to know that your luggage is safe at any time.
Overall; good experience; would definitely go back if ever i would visit San Francisco and stayed on a budget.
but remember its a hostel and not a hotel; so you get what you pay for~