I went there for lunch today - they were doing a brisk business. It'll take a few more visits to really get a sense of the place, but initial results are encouraging.
I had the Spiced Seasoned Fish hot pot (because this was my single favorite dish on Nam Vang's menu) - XX's implementation was different, in that they used salmon instead of catfish (though I seem to remember Nam Vang offering me a choice once too - maybe I'll try asking for catfish next time?) and the sweet/spicy sauce was thinner than Nam Vang's - possibly the same volume of sauce to start, but reduced less? It was also spicier than Nam Vang's, and spiciness almost always wins me over.
My companion got the fish balls noodle soup, which she said was very good.
Staff are friendly, and eager for feedback - service was a tiny bit slow, but considering they've only been open for a few days, and were full, it was pretty impressive.
Prices are higher than Nam Vang's were, but if that's what it takes for them to make a profit, I'm game. (Nam Vang, wherever you are: I would've paid more for the spicy fish hot pot, and done it with a smile, if you'd only asked)