I'm from Yunnan and I think this place is quite authentic. The cross bridge noodle has the right tasting broth (similar to what you would get in Kunming). Another must is the fried potato. Now this is not your typical fries, this is Yunnan street food! The secret is in the sauce, which has a special bean paste from Kunming (????), fermented bean curd, and cilantro. Not extremely spicy, but it is very savoury. One thing I see other people complain about is the sogginess of noodles - these are rice noodles and can't be compared to the chewy ramen!
P.S. try their home made Yunnan moon cake too. It is different from Cantonese style moon cake. Stuffed with salty and sweet ham, these moon cakes really compare to the ones I used to eat growing up.