We visited this bar once while we were touring Warsaw. It was conveniently located around the corner from our hotel. The atmosphere was relaxing and fairly inviting. The bartender was pleasant and, fortunately, spoke English. Many of the patrons seemed like locals and many were also speaking English.
We sat at a table overlooking the street, so we didn't interact with any of the other patrons, They are clearly used to have foreign guests in the bar, so we didn't feel uncomfortable. They do serve food as well, but we didn't eat.
Definitely a nice, relaxing place for an evening drink.