Overall we had a good time in Mario's apartment. The location is perfect, it is only 10 minutes walk to the Ponte di Rialto as well as to Piazzale Roma (bus station). Right under the flat is a restaurant, where we had pizza and I can recommend the place.
I would appreciate If there was more towels available. We were three people and there were three towels, so no towel for hands.
The only thing I found odd, we pay for cleaning service but you have to do the dishes and take out your trash before you leave, otherwise you will be charged extra for "additional" cleaning. I also find confusing that in some photos you see a coffee machine and kettle but neither one was in the apartment.
Also be prepared to pay a tourist tax (currently €4 per person, per night for the first 5 nights) and to provide your ID's details (requested in Intaly everywhere).
If you are considering going to the beach for swim, I wouldn't recommend, it is not worth it. We went to Spiaggia libera/free beach and If you want to use showers, toilets or changing room you have to pay for it. The sea was not clear and I got burned by jellyfish, which I found out it is usuall over there. I would still go to see the island and maybe for walk on the beach but definetely no swim again!