This is was a great place to stay, and the hosts are wonderfully helpful. The apartment felt a little larger than it looks in the photos, and careful help in checking in and explaining how to make the most of the city were both really appreciated. They really went beyond the call of duty by even printing out boarding passes for me :)
The location of the apartment, between St Mark's Square and the Gallerie dell'Accademia, is really perfect. It's a couple of streets off the beaten track, so very quiet, but also wonderfully placed to make the most of both San Marco and Dorsoduro.
I had considered taking a slightly cheaper place that was less well positioned, but I certainly made the right choice in renting this beautiful apartment.