It's not express but it tastes good! I find it fairly difficult to find a Pho place out in Vegas that tastes authentic. Rainbow Pho Express is pretty authentic! Reminds me of the Pho places I love back in San Jose, CA where you know Pho is authentic because of the number of Vietnamese residents that reside there.
My go to items to order are of course the Special Combination Pho soup, fried egg rolls that come w/ lettuce to wrap and dip in the fish sauce, and my ultimate favorite is their vermicelli bowl equipped with grilled shrimp and fried egg rolls. Their rice plates with pork chop is real good too. Everything is flavorful here and I love their Pho broth; there is no need to add sauces to it, just some lime and jalapeno for a little kick! They have an abundance of veggies in their vermicelli bowl which is why its my favorite!
I knocked off a star because they don't have very many chicken dishes, or none at all on their menu which I find weird.
Overall, great place to go. But be warned, it ain't express!