The flat is spacious with lots of light and all of the basic amenities, including a large comfortable bed, and a close walk to everything you'd want to see in the city center. Charlotte has stocked the living room shelves with maps and pamphlets of sites and tours in Vienna so you can read up on things to do if you don't already have a packed itinerary. Charlotte leaves clear and easy instructions, including emergency contact information on the dining table in the large living room with keys that are easy to operate, and a lift for getting your large bags upstairs. The stairwell is easy to climb, and flat easy to locate. The apartment is meticulously cared for, and spotless when we arrived.
The only downside, beyond Charlotte's control, is neighboring flat occupants must smoke in their flat, as there is a noticeable but faint transference of smokey odor. I'm particularly sensitive, so it is most likely not obvious to most, and Charlotte advertises a strict "no smoking" clause for her flat, which shows in quality, cleanliness and is greatly appreciated.
Overall, I'd recommend the flat as a place to stay while in Vienna, as Charlotte was highly communicative and prompt with both communication and arrival, even with short notice when our travel plans changed and we arrived earlier than expected and I forgot to let her know!