We stayed for less than a week in Mario's apartment. It was great, very close to the city centre by bus, and about 20-25 min (or less) walking so it is perfect If you fancy to have a morning walk before visiting the Old town.
It is located in a residential neighborhood but full of lovely restaurants and life at daytime, we also could find some places to go and have a drink in the evening. You can find a supermarket at less than 5 min from the apartment so it's pretty easy to buy anything you need for your stay. About the apartment, it was decorated as nice as it is in the pictures, very confortable and clean.
Mario was very nice and always ready to help us in whatever, he even prepared a document explaining some information about how to use the kitchen stuff and everything, also a tourist guide with the "must visit" places.
I recommend his apartment for a lovely holidays in Edinburgh!