You not only have to be careful because of the fish sauce (for example in s06 which was my favorite food a while back before I learned its "special vietnamese sauce" contained fish sauce; now I have to eat it with soy sauce instead and that tastes like half that good) but also the coconut soup contains cows milk which they won't tell you unless you ask explicitly and they also sometimes are that stressed they do not bring you tofu but meat. They do not get veganism so they also don't get that you may be a vegetarian or vegan when asking for tofu instead of meat and don't mention other non-veg* ingredients.
The atmosphere is nice but the place is so crowded you often have to wait a bit in the evenings before they seat you - next to other people with free seats on their table. YEAY for meeting new folks unintentionally at dinner!
The staff is like always stressed and not that friendly but also not impolite.
Otherwise: The meals are super cheap with 5.50€, that's a good deal for the quality and I never go home hungry. And drinks also are inexpensive. If you do everything right you will surely enjoy your meal.
Cons: be careful while ordering, crowded as HELL!, don't expect nice staff