We enjoyed our week stay at Ana Maria apartment very much. Staying there allowed us to be in the middle of everything and to get feel of the real Venetian life.
Check in was easy, we received detailed and easy to follow instructions how to get to the office, a block away from the apartment, where check-in actually happens. Then we were escorted to the apartment. Apartment is very spacious, impeccably clean, you'll find all the essentials in the kitchen, including olive oil, salt and pepper. Milk, yogourt, a bottle of water were waiting for us in the fridge, we did appreciate it! There were also coffee pods for the coffee machine.
Location is perfect, around 300 m from San Marco vaporetto (water bus) stop, just 100m from San Marco square ( you can see the tip of San Marco Campanile from the kitchen window), lots of places to eat around. Unfortunately, there are no grocery shops in the vicinity, if you stay for longer you'll find them, but there are two by Realto bridge for a start. Realto market and Realto fish market definitely worth visiting even just to take a look.
I wouldn't call it downside, but be aware that the apartment is in the third floor without elevator with very steep staircase.
I would highly recommend this apartment for your Venice experience.