Unless you are afraid of stairs, I can see no reason to not book this place. I don't think you can get any closer to San Marco square! Very friendly and responsive hosts.
Because of renovations elsewhere in the building (that didn't further impair our stay) wifi was down, but that was no issue for us. If it would be for you, I suggest asking ahead of time to make sure it is fixed.
We would be delighted to stay again!