Great location, great views of Edinburgh Castle. No need to rent a car as a of lot of things to do is in walking distance and transportation is at your figure tips.
Bed was comfy, a bit small but worked for us.
The 54 stairs to get up to the 3rd floor was a bit much and we are in pretty good shape.
The bathroom was small, sink was very tiny and hard to wash your face without getting water on the floor. Shower was small as well.
If your going to stay more than 3 days, you may want to ask for more bath and hand towels as they don't provide or stock them in the apartment which they should.
All in all.... the apartment is in a wonderful location.