My husband and I had an enjoyable stay at Justina's apartment. We were looking for something located on a quieter street, away from traffic noise. Justina's place is perfect in this sense - it is located on a smaller, quieter street, so it is guaranteed that you will not be bothered by traffic noise. However, be prepared to hear some noise from the apartment upstairs (it appears as though insulation between the floors is not great, so we heard it when people in the apartment above were walking around).
Another reason why we really liked the location of the apartment is that it's very close to tram/bus/metro stations. We could easily travel everywhere in Vienna and the public transportation system is wonderful.
The apartment is very clean and functional. The kitchen is small but it comes with everything you need to make a simple meal (the only thing that we felt was lacking was a microwave). There is also a cozy private terrace, but, sadly, we were not able to use it as during our time in Vienna the weather was not great for sitting out outdoors.
Overall, we had a very good time staying at Justina's and recommend this apartment to other guests.