They are all related and owned by the same family, though I don't know if I would classify it as a chain - at least not in temperament or vibe. We Nolita locals are bereft of having lost such a prime spot for hanging out and people watching, and feel rather displaced that the place is gone. We called it the black hole as one could spend hours on the porch in the summer.
While not a culinary temple, a few of the dishes were quite good and very consistent (chicken/papaya salad, fried calamari), though I don't think it would necessarily be considered authentic.
The new location is quite a bit smaller.
R.I.P. to Mekong on Prince indeed. My best girlfriend and I would stampede over there for the beef carpaccio and cocktails every Friday after work. That place was so good -- soft shell crabs were to die for, and they could handle their noodles pretty well, too. Surprised to hear that the Pho was a let-down, but it is a fusion place so the classics do bear reinterpreting.
I understand that it is a chain...I'd check it out. Let us know how it is! I still drool sometimes when I think about that carpaccio (it was more of a beef ceviche...ginger, scallion, lime, etc.).
I've gotten take out there. It was a seitan dish, wasn't quite what I expected it to be but decent just the same. Not fabulous ... decent. Don't know if it's the same owners as the Slope Mekong; the man who owns this one used to own the Mekong on Prince St in Nolita ... I know because he recognized me from there ... very surprising because that was over 6 yrs ago.