As an update, I did try Bianyifang. I thought the duck was quite good, but it didn't knock my socks off. Indeed, I thought the duck I had at Xihe Ya Ju on the edge of Ritan Park was more enjoyable. It could be because it was a nice night and they offered outdoor dining, though.
FWIW, Ritan Park also has a branch of Xiao Wang's, which is another excellent restaurant. Xiao Wang also has good duck, but Xihe Ya Ju's is probably better.