First, the great: the location is AMAZING. It's easily accessible, a nice street, and the ideal home base for time in Venice. There's a washing machine, which is really nice to have available, and the space isn't cramped.
Second, the not-so-great: the bed and the smell. When we booked it, the listing indicated a real bed, not a pull-out bed from a sofa. Closer inspection of the photos reveals it is, in fact, a sofa bed. Actually staying there reveals it is possibly the most uncomfortable sofa bed in the world. It curves uncomfortably, is very flat, and is pretty short (my husband and I are 5'10" and 5'7", respectively, and just barely fit). The entire place also smells musty and faintly of old cigarette smoke, and it's very dark. Opening windows does not help the smell, and if you use the laundry machine (or even just want to dry the towels provided) you're in for a long wait for anything to dry off. While the pictures look light, the space is very dark, which increases the feeling of being in a vaguely unpleasant cave. If you want to stay here for the location, go for it. Don't expect this rental to be a nice place to return to and relax, though. If you can find somewhere else to stay in this neighborhood for a similar price point, I'd do it.