Erika's apartment is well-located and nicely decorated -- looks like the photos. It is about a 7-10 minute walk from the Duomo and 20-25 minutes from the Santa Maria Novella train station. We enjoyed the large supermarket a couple of blocks away. The washing machine was convenient. The stairs were manageable for us 30-somethings: I thought of it more as 2 flights of stairs, with 2 returns per flight, but you can think of it as 4 flights if you prefer. In any case, they did not particularly tire us out going up and down them multiple times a day. The host was very responsive and even dropped off additional toilet paper for us before she took off for holiday.
We stayed there in the heat of mid-August. We did feel the air conditioning was not strong enough due to its placement in master bedroom, which is are two hallways (with a turn) away from the main living area. It was comfortable in the bedroom, but my family who slept in the living room and smaller bedroom reported they were extremely hot every night. Some more powerful fans should improve the situation and also help circulate the air from the master bedroom to the living area.