The apartment is a good size. The views out from the lounge and bedroom are stunning and the lounge / kitchen is also a good size.
Bedroom and bathroom are basic, but functional, which is all you need.
Be warned about the stairs up! There are a lot! We were fine, but if you have any mobility issues then you may struggle with cases etc. I'd also question Edinburgh itself as the city is far from flat!
Maureen was incredibly helpful, with detailed instructions provided and she was always on the end of the phone.
One grumble, which we were probably unlucky with. On the Wednesday and Thursday of our stay, there was a group of kids (approx 40, possibly European due to accents and singing happy birthday at 11pm) on the grass opposite celebrating a birthday on both nights. They were noisy till the "wee small hours". Then on the Thursday morning, there was a girl coming back from the pub making a scene on the street at 3am, which woke us. Strangely, the Friday night was peaceful, so I suspect that we were just unlucky as nobody else seemed to have issues and the secondary glazing in the bedroom does block out most 'normal' noise. The general noise from the local grassmarket area was fine.
Overall, the apartment was lovely and a great location to explore the city.