We visited Dusseldorf recently and were lucky enough to find Jade. If you're in the area as a tourist, it's about twenty minutes on foot from the Friedrichstadt district, and the route is through a more residential part of Dusseldorf. The route along Martinstrasse also allows you to see two lovely churches as you walk to and from the city centre.
As for Jade itself, the food was excellent. It was a pleasure to have so much choice on a single menu. Everything was cooked after the order was placed and was completely fresh, but they were also very quick. We were not kept waiting, as might be expected with made to order dishes. The prices were also excellent; we had drinks and a three course meal for less than thirty euros. The staff were friendly and the service was good.
I would suggest trying the vegan crackers as a starter, and my husband said the banana fritters with agave syrup were the best he can ever remember eating. The restaurant is slightly out of the way, but it is well worth a visit.