We ate at Kostlich once and liked it more or less.
It was very crowded (there isn't much space to sit, just four or so little tables) and not very cozy. It seemed that mostly business people came to eat there which isn't a bad thing of course.
The vegan dish of the day were vegetable wraps with tofu and a lentil-chili soup. A big portion (two wraps) cost around six Euro - too much if you ask me. It tasted alright but wasn't the best thing I've ever eaten and didn't fill me up completely either.
For vegan desert there was banana-chocolate cream with coconut and rice pudding. I wanted the first but unfortunately it was gone already so I decided to stay with my - delicious - strawberry juice.
The staff was very friendly and helpful.
We paid around 20€ for two people.
If you are around in the area it's ok to give the place a try and see for yourself :)