The flat is as central as you could want to be without actually staying on the Royal Mile. We stayed in Fiona and Neil's flat for a month and had a great experience. We walked almost everywhere. There are tons of restaurants and other entertainment nearby. The flat was spacious and comfortable, especially the beds. The kitchen was well appointed for cooking and everything was very clean upon our arrival. Neil was extremely responsive and a fantastic host! The check in and check out process were easy and seamless.
The only downside was hearing the neighbors above us walking around at all hours of the night and late night noise from the nearby bar. We adjusted fairly quickly to the noise and had a sound machine app on very loud throughout the night, so it wasn't too big of a deal, but it's worth mentioning if you're sensitive to that kind of thing.
Overall we had a fantastic stay and would definitely recommend it!