If you look up best Vietnamese restaurants in Berlin, there's a few recurring names and Cowei is not one of them. There are located along a park next to the river Spree and so they'd probably get business regardless of the quality. To be fair they don't advertise as a Vietnamese restaurant and the menu has sushi, bits of Korean, and bits of Thai.
The inside has a picture of Ho Chi Minh. It represents the restauranteurs' heritage from Northern Vietnam.
Hanoi has arguably the better pho in Vietnam and its quality was represented well in this restaurant. A delicate and crystal clear broth with wonderful flavour balance and decent beef brisket. Interestingly they don't use raw/rare beef sirloin dropped in and I would have liked extra Thai basil, but I can hardly complain. It was excellent.
Unfortunately the other dishes didn't live it up. The crispy fried duck red curry did indeed have thin cuts of crispy fried duck, but the red curry was not red and had none of the flavour and heat that a good Thai red should (considering Viet curry is simple and not spicy at all probably influenced this...). I didn't try the chicken salad dish but the Vietnamese mother I was with strangely selected the mango sauce, which she then complained wasn't a Vietnamese thing - not sure what to make of that. The other Vietnamese salad dish (unpictured) did not have a good balance of the dressing sauce, with it being too dilute and vinegared, possibly contributed by the water from lettuce draining into it.
I'd go back for the pho but stay clear of everything else.