We were coming to see the Biennale so the Location of Mario's place was perfect, right beside both the Giardini and the Arsenale. If you are coming at a different time of year and want to explore more of Venice, this location might not be the most convenient. We loved how local and non touristy it felt and there are many great bars and restaurants on the Via Garabaldi.
Mario's place is very clean and has everything you need. However, arriving late on a November night when it was cold and raining, it did not feel very cosy ... there are no lamps, the lighting is very harsh and there was not even a rug to soften the cold tile floors. This is a minor complaint, we bought some slippers and a candle and that helped the place feel more homely!
Apart from this everything was very straightforward. Be aware that you need to dispose of the rubbish before you check out and that is not that easy in Venice. We found a friendly garbage man on the street the morning we were leaving!