Great property, and staff were very responsive and helpful in answering questions and helping (like storing luggage). We could walk to almost every tourist spot in Edinburgh in 30 minutes or less (Holyrood maybe 40 minutes). Public transportation (trams, busses) is right outside the door.
The flat was very comfortable and fitted out well (though it would have been nice to have some basics like salt & pepper, cooking oil in kitchen). It is at corner of Charlotte and Princes streets which are very busy streets. You could hear some noise, but with double windows, the street noise was pretty mild. My wife is fairly sensitive to noise, but with simple earplugs, she was fine for sleeping.
One other thing. You need to be able to climb stairs. These stairs were wide and easy to manage even with luggage, which is not always the case at other places in UK.