This review is based on a 4.5 month stay from February to July, while working abroad.
Renate's place is fully featured and is suited for a single person or a couple, using the large sofa-bed, or for a couple + an adult/kid, also using the spare bed. Through living there in an everyday-life situation (normal working hours), I find the apartment both functionally well laid out and cozy/homy. The bathroom (with a washing machine) and kitchen (with a dishwasher, a two-place cooking top and a microwave/grill oven) are clean and of modern standard.
The apartment is located in a high ground floor, on the shady side of the street, but there is plenty of light in the mornings. Notably, the apartment was cool and refreshing in the warmer months, and in the colder months, the gas-driven water boiler/radiators furnishes efficient heating and hot water supply.
The location in the 9th district is central, yet withdrawn from the bigger/noisier streets, and getting around central Vienna is easy with collective transportation by buses, tram, subway and some railway options close-by (Franz Josefs Bahnhof was under construction during my stay, but is just 2-3 blocks away. I'd still recommend getting a bike, as this makes getting around quick and easy, with most places in the central districts within a 15-20 min bike ride. In the end, there are many interesting districts in Vienna, and where it will suit you best to stay will depend on what you are there for and for how long (my place of work was in the 9th).
Renate is an attentious and friendly host - communication with her was always pleasant and expedient!
I can wholeheartedly recommend her place for future visitors to Vienna.