I've been to Khai Hoan two times now. The first time I got the number 5 and the second time I got the number 15. Both were excellent!
The service is fast, we didn't have to sit at the table for long before someone came over and took our order. Even getting the food didn't take to long. The beef in the number five was perfect, sliced thin and rare when it was put in so that the broth could cook it.
The broth wasn't overly oily and you get a big plate of 'fixing's (like bean sprouts, lime and basil) for your soup.
Overall, this place was great--though I think the soup needs more meat on average.
I will go back for sure!