The combination of price and location is very good here. The place is just a couple of metro stations away from Karlspatz and Opera, so you can ignore metro and take a 20-min walk through Nashmarkt grabbing some breakfast on the way (and it's amazing).
The apartment itself is small but has everything you need for a three-five days trip. Suitable for three people, but perfect for two.
Stefan himself is very helpful, and if some problem pops up, he's ready to solve it immediately. Recommended!