I regularly go there between university classes (it's very close to Vienna University). They offer special "student plates" which are of great value: for €5,50 you get a huge piece of a vegetarian or vegan casserole of your choice with a decent ladle of sauce of your choice and three salads (also of your choice). They also have daily changing lunch menus. Considering the big portions, the regular prices can be considered cheap too.
The salad buffet includes more than 10 different fresh salads, most of them are vegan and all I've tried so far were very tasty. Recently, they started selling a variety of vegan cakes too. The staff is super friendly. Unfortunately, there is only a very small seating area but you can take away all of the food too.Pros: healthy, tasty, diversified food, huge portions, great value, very friendly staff
Cons: very limited seating