FiDi banh mi stands [San Francisco]

I noticed a small banh mi stand on Main, just off Market. Pretty simple: banh mi (four of five different fillings), spring rolls and drinks. Bahn mi were $3.50. I'd just had lunch or I would have tried one. Woman said they are there M-F 9:30-2 and that she also has a stand on California St a couple of days a week.

Any experience with these? (Tried search -- terms too common!).