I spent 10 days at Elisabeta's apartment, it was my first Airbnb stay and an excellent experience. The apartment itself is small but had everything I needed. Good bed and clean linen/towels. The heating worked (it was unseasonably cool for April) and there was a small portable radiator in the bedroom besides. Likewise I had hot water to shower and the water pressure was good. I'd love to have the heated towel rack back home! The lighting wasn't strong at night but that's about my biggest complaint. Be aware that the kitchen is basic (no toaster, microwave or oven) but there's a fridge, stovetop and coffee maker, dishes, silverware and cups. Also no TV and the hostel wifi isn't strong enough for streaming, but that's a fair tradeoff given the very reasonable price and you can get a tourist SIM card plan (TIM or Vodafone) by the Santa Novella station for cell phone data.
I was a little nervous about the hostel beforehand but the apartment is separate and it wasn't noisy. You do need to go through hostel reception to go in as the key is only for the apartment itself. If the reception asks you for the key when you go out it's because they think you're staying in the hostel, so just remind them you're at the Residence. I'd definitely recommend not overpacking like I did as there's a bit of a path to the apartment including stairs (special thanks to the receptionist who helped get my suitcase up first day). Going through the monastery courtyard with its painted frescos each day was itself a special experience you couldn't get elsewhere!
The location itself was truly terrific - steps from the Arno, in between the Ponte Amerigo Vespucci and Della Carreira. Many great places to eat are across the river, so it was very convenient (tip - go to Gelateria Della Passera and try the Mona Lissa.) You can walk just about everywhere within 30 minutes. For groceries there's a Conad about a block away.
Elisabetta herself kept in touch during my stay to check that all was good and wish me a good time. I'm sure she'd have been responsive if there was a serious issue. Overall I can easily recommend and would be happy to return. Thank you Elisabetta for helping me have a wonderful trip!