We stayed in Mario's apartment for 4 nights at the end of May (wife, 2 teenage daughters and myself). In the run up to staying there Mario's communication was superb - responding to any questions quickly and giving very clear responses.
When we arrived at the apartment we were met there as planned, and shown round the place. Good clear instructions on things like the bin collection, etc. Apartment was spotlessly clean and well furnished. Lovely views over the rooftops of Venice. Only comment we would make is that it did get too warm at night - the aircon is not great.
Location wise it couldn't be much better. Everything was in easy walking distance but the actual location was quiet from the noises in much of the city. Supermarket 50m away, good selection of restaurants and shops nearby. And Venice itself is spectacular - great place to visit.
We would thoroughly recommend Mario's apartment for a place to stay when visiting this cool Italian city!!