My wife and I have spent two weeks at Isobel's place. It is a two-storey flat located at the third floor. The first storey contains a shared kitchen, your bedroom (adjacent to the kitchen) and the private bathroom (accessible from the bedroom). The second storey is the Isobel's area. The shared area is shared with the host (she was out of the apartment, besides the two days when she had some business to do in Florence). It might be quite an inconvenience if you like privacy so take it into account during booking.
The location of the place is excellent. The piazza downstairs is lively and feels very authentic, yet it is not too noisy and if you close the windows during the night you can comfortably sleep (the main square in the city would be much harder to bear). The contact with the host (Isobel) is very good. She offers help in most situations that you might encounter in the city (or Italy in general). You should be aware that it is an old building and there might be some issues with the plumbing. Therefore, some odours might be uttered from the pipes. After 5-6 days of our stay (in the middle of August) the smell stopped to be a problem (probably the pipes were properly watered and prevented the smell to come out). Opening a window in the bathroom somehow helps. Yet if you are sensible to such things, keep this in mind when considering the place.
The apartment is fully furnished, yet it required a bit of tidying in the kitchen when we came in. It was also a little bit disappointing that the washing machine was not available at the apartment, as the rules were changed some time after we had booked. Isobel was so kind that offered us to do some laundry (towels and some clothes) but it would be much nicer to have this to your disposal. It is even more important if your stay is longer (we stayed there for two weeks) and the washing machine was a thing you were looking for during apartment selection and then booking. Otherwise, the number of available towels should be counted in such a way to cover your stay.
To sum up, it is definitely a good value for money in a very good location, but we wouldn't call it "luxurious" as in the description.