The apartment is 5 min walking from the train station, and about 20-30 min from piazza San Marco (much less if you take the boat). It is located in a quite neighborhood (Jewish ghetto), but anyway close to all what you need (restaurant, shops, supermarket, pharmacy). The apartment is clean and well furnished. If you're taller than 1.75 m it could be somehow uncomfortable... Bare in mind that the door frames are low.
The host is really kind, and very supportive to all the questions and needs you might have before and during your stay. I would recommend it for two people; four is also ok, if you don't stay more than few days. Anyway you should not spend too much time in the apartment if you visit Venice!