When it comes to ethnic restaurants, there are a couple of rules that I like to follow: (1) generally, you want a no-frills establishment. There are basically only tables and food there. (2) The more of the clientele that is of the same ethnicity as the good, the better! For more similar rules, you can check out "An Economist Gets Lunch" by Tyler Cowen; it's a bible for finding cheap, high-quality ethnic restaurants.
Pupuseria La Bendicion definitely meets both of those criteria. The menu is very straight-forward and everything tasted wonderful. I didn't love the refried beans though; they were sort of dry and the texture was not as smooth as I would like.
Overall, this place is wonderful for quick, cheap, absolutely tasty eats. Highly recommended!