Catriona's flat is located very close to the old town and a short (10/15 minute) walk from the airport tram, however you do have to walk down a very dark alley to the front door, which could be scary to do alone.
It doesn't look as nice as in the photos, it's pretty worn in places and quite dirty throughout (dust on floor, dirty bowls in cupboard, black shower). The tv photographed is actually about 19" and attached to the wall at the end of the room so almost impossible to watch from sitting on the bed, also it only has catch-up services, no aerial connected. The 'king-sized' bed is actually 2 singles pushed together, so there is a slight ridge down the middle where the 2 mattresses meet. As annoying as this is though, the bed is otherwise comfortable and the sheets are clean.
The alley that the flat is on has a nightclub at one end and the surrounding roads are popular with the university students as other people out drinking throughout the night, I was woken 3 out of our 4 night stay. The walls are paper thin and you can regularly hear the neighbors.
As mentioned by other reviewers the shower isn't very powerful, and when it is, it's very hot. The heating in the flat is very good (once Catriona sent someone out to turn it on for us!).
All in all, Catriona's flat isn't a bad place to stay if you're looking for somewhere quite central and you're visiting Edinburgh for the nightlife or plan on being out a lot and just sleeping there. Otherwise we just found it a little bit too worn and loud for our tastes.