The location is amazing. You can literally see Haymarket station from the window so we didn't have to go far with our luggage. There is also a tram stop right outside and bus routes to and from almost anywhere. If you are fit it is also an easy walk to the centre of Edinburgh. The flip side of the location was that it was a bit noisy as the trams start early in the morning, but we were sweetly left complimentary earplugs which was a nice (and needed) touch! Personally I slept absolutely fine with the earplugs in.
Assean was a perfect host. While we didn't get to meet him personally as he was away, he arranged to have us met at the flat and always answered messages immediately. There were provisions left for us in the kitchen.
The rooms are nicely decorated and comfortable and the flat is stylish. The floors aren't carpeted which makes the place feel fresh and clean, but again it amplifies the noise of people coming into the flat late at night. Since that person was usually me I wasn't bothered by it and the rest of my family didn't complain much!
There is no communal living space other than the kitchen which is small for the number of people who could be staying there (up to 10), but we weren't in Edinburgh just to stay in our flat. One of the bedrooms is very big so we made that a shared space when people weren't sleeping there. Also there is only 1 bathroom so be prepared to queue for the loo!
Whilst pricey, as all Edinburgh accommodation is during the Festival, it was exactly what we needed for a big group to stay and to have a great time.