First things first: the key reason to go for this flat is location. If you want to be at the centre of things in Venice, 2 mins from San Marco Square and with easy water bus access, you can't get better than this. You're also right by several good restaurants and cafes and a 10 minute walk from a Coop for the necessities.
However, because it is in the centre you will experience VERY high noise levels through most of the stay (and late into the night). So if you are sensitive to noise, definitely bring a good pair of ear plugs for sleeping.
Flat is clean, has all the basics and decent beds. Wifi works well (in the living-room) and the host is very close by if you need help. They provided soap, shampoo, a hair dryer and towels for us. The flat is also well-heated (we went in midwinter!).
As I said, the main draw of this place is location. It is super-central.