I'm a connoisseur of Vietnamese food, especially Bun, and this place has the best I've found in downtown SF. The grilled pork in the Bun Thit has a nice slightly sweet flavor and they put a fair amount of mint and veggies in to boot. The fish sauce.. well, it's fish sauce. I wouldn't drink it, but it tastes good mixed up with the noodles.
The Vietnamese coffee is good, but I can't say I've ever had a bad one.
Decor? We're talking hole in the wall Vietnamese here.
Good food for under $5.