So, you need to know what you're getting into.
First of all Andreas was both very responsive and very accommodating. He let us park our car at the apartment before check-in, and offered for us to use his parking pass in downtown Vienna. He also provided helpful instructions on using public transit. He was a fantastic host, among the very best.
The place itself is just barely acceptable. It is smaller than it appears in the pictures. The hallway between the toilet/bathroom/bedroom doesn't have enough room for two people to pass by each other. The bathroom and shower are tiny.
In general, the place fields...not dingy, but old. The important things worked, but everything was as utilitarian as can be and very basic. The windows were difficult to open and close due to malfunctioning mechanisms. The beds were not comfortable. One of the wall heaters was missing a knob and could not be turned off. Several light bulbs were out. No deal breakers, but not in great shape either.
The location is also pretty far from downtown Vienna. It took us 45 minutes to an hour to go from front door to the Vienna Opera House and back. The neighborhood itself felt safe and was well-lit at night.
However, I still give this place 4 stars because of the pricing. Other places I was looking at were much nicer, but 2x as expensive. If you just need a place to sleep and don't much care about spending any time at the house, you'll be hard pressed to find a better deal. This place would work well for a couple of nights' stop in Vienna, but I would not consider it appropriate for a longer stay.