See here

You should expect some inconvenience if without a car. Going to BART/CalTrain by Scooter isn't bad idea compare to a bike. but I'll still prefer biking. However, since Potrero is up and down some blocks are really steap slope. Homeless are seen in some areas and along 3rd Street. BTW, if on 3rd St, there will be traffic during game days (Chase Center Basketball or Baseball in ATT park), Lots of young tech guys get in Potrero in recent years, property appreciated a lot. If with out a car and rely on BART, I'll avoid this area, unless have specific reasons such as working in UCSF Mission Bay Campus, etc. Also avoid 3rd Street apartments if you can, even though it is up and coming area. Bayview and Hunters Point are extended areas from 3rd St., some bad apples will show up along 3rd St.

Let me know if I can be any more help.