Mario's apartment is a fantastic value and looks even better in person than in photos. The biggest plus is its location. It is close to the train/bus/taxi station (10 min walk), so it's easy to find on arrival, much closet than San Marco. It's also about 10-15 min from San Marco. This means it's very easy to get to the tourist attractions there, but still have accommodations in a nice and quiet area. This area has a noticeably local and authentic feel. Also, the restaurants in the area are absolutely great.
I'd recommend this space to anyone traveling to Venice!