We had a great time at Gerti's, we would absolutely reccomend it and come again next time we're in Vienna.
Sometimes there were other people in the kitchen and/or bathroom which could make it difficult to cook and go to the toilet if you're in a hurry. The curtains were a little hard to close and they let through a lot of light, so if you're sensitive maybe bring something to cover your eyes.
Apart from this we had a wonderfull time. The apartment has a very roomy feel and there are lots of grocery stores in the neighberhood. It was about a 20minute walk from the city center. Gerti was very accomodating and offered us cornflakes, butter, tea etc. for breakfast.