Luz was out of town and a friend met us and explained everything, then followed up with a message to check that we had no problems. Communication with Luz, both before and during our visit was excellent. During our stay of two weeks, when we had a problem with the hot water, Luz's husband returned from Milan to sort it out, so you couldn't ask for better service.
For us, the apartment was great, perfectly located in a more residential area, but still with plenty of restaurants, bars etc. A good sized supermarket is at south eastern end of Campo Margherita, only a few minutes walk away. (Not easy to see the first time, but opposite a gelateria, which I think is called Doges)
Closer that that, on Calle S. Pantaloon, is a little shop that sells milk, juice, water, cheeses wine etc , and an ATM next to Church S. Pantalon. All the nearby shops and eateries seemed, to us to be more reasonably priced than near St Marks.
The apartment is an easy 10 minute walk from Piazzale Roma, about the same to the Accademia and Rialto Bridges. We were able to walk everywhere and only used a vaporetta when we visited other islands.
Everything worked well in the apartment - the WiFi, dishwasher and washing machines and central heating. the bathroom and kitchen are both small, but perfectly adequate.
In short we had an excellent stay. (The only reason I gave one less star rating than the maximum, is that I reserve that rating for luxury places)