I'm Vietnamese and I think this place is one of the more authentic places for Vietnamese foods. That being said, authentic doesn't mean it's better. To be honest I like the pho from those chain pho restaurants better, but those pho places are the equivalent of McDonald's for "white food": they taste good, but they aren't authentic.
The pho and noodle soup dishes at MiMi's taste a lot more like what my mom's pho and noodle soup dishes taste like.
What I go to MiMi's for, and what it is known for are their BBQ vermecelli dishes! Their vermecelli noodle with their BBQ beef, beef balls, Vietnamese sausages, shrimp/seafood wrapped around sugar cane with the fish sauce - that's the stuff! It's fantastic! If you go to MiMi's, I would strongly recommend their Vermecelli dishes.
I also eat their rice dishes, they're good too. And yes, there seem to be a lot of white people in this restaurant for some reason... but I think that's because it's a slightly nicer looking pho place and the waitress there is really friendly and speaks English fluently (as well as Chinese and Vietnamese) - which is impressive!