We have been there twice, without booking a table in advance, and both times the restaurant was full. Last time we had to sit in the backyard, altough it was too cold for my taste to sit outside, as indoors was full.
They mainly offer "faux meat" dishes. I ordered the Satan Burger and my partner the Bratfilet „Art Leberkäs“. My burger was extremely tasty, the seitan "Bratfilet" wasn't really to our taste, we've had much better "faux meat", the rest of the dish was ok.
Furniture in the backyard was basically those wooden tables and benches you find at village fairs, which were very uncomfortable.
Cons: portions are quite small