My friend and I spent two weeks at Roy's place over Christmas and New Year and it was absolutely spectacular; so much better than I could have hoped. The flat was clean and well decorated and Roy had thoughtfully put up some holiday decorations and left us a bunch of chocolate and some prosecco for our enjoyment. Additionally, Roy left a packet on the table that contained some useful information on nearby restaurants, pubs, and grocery stores which came in handy several times throughout our stay.
The flat and all the linens and towels were very clean and the amenities were perfect. The kitchen is very small but there is enough room to cook almost anything (we cooked Christmas dinner and Roy helpfully provided us with a potato masher when we asked if there was one in the flat). The washer and dryer work well and we were able to do several loads of laundry throughout our stay. I cannot speak to the dishwasher as we never used it since we washed all our dishes by hand.
The sofa bed is quite comfortable and easy to use and there were plenty of extra linens in the chest of drawers in the bedroom to use on the sofa.
The only issues I can think of related to this flat are that it can be a bit noisy due to traffic on the main road just outside and you occasionally get odd odors emanating from what I assume are the neighbors' flats. People sometimes honk and ambulances go by not infrequently. If you're a light sleeper like me I'd suggest bringing ear plugs. The smells come around at unpredictable times and it was always either an incense/pot odor or a heavy floral air freshener-type smell. Opening the windows helps. Also, if you don't do stairs well, this is probably not the place for you as there are no elevators in the building and this flat is on the third floor.
If you're looking at this flat for your stay in Edinburgh I would absolutely recommend you book it. Roy was a fantastic host and the flat itself is wonderful. There is a bus stop right outside with buses that go directly to Princes Street and the airport which is extremely convenient.