Excellent place for a young female solo traveller! :)
The location and value of the apartment are great! It has all of the basic amenities you need for a city trip and the decor is cute as well.
If you are on the taller side, the space might not work for you - I'm 5'2/160cm and I was able to touch the ceiling without fully wtretching my arm. To me, the space felt cozy rather than cramped.
There is also very limited daylight due to the type of older building the apartment is located in. I really only spent time inside for sleeping and taking showers, so that didn't really bother me.
The apartment is located right in the heart of the city, in the historic center which is bustling with activity most times of the day and even night. So if you are a very light sleeper with an early bedtime, bring some earplugs.
There is also an elevator in the building, but you have to be able to take the stairs to go up or down one flight of steps to reach the mezzanine.
As for the neighborhood, I'm a smaller woman and was travelling solo, yet I never felt unsafe walking back to the apartment at night. The entrance is in a quieter side street leading right onto Via dei Tribunali. I spent most of my evenings in the Centro Storico and the areas more frequented by tourists. From there it's only a short walk op the street to the apartment building.
Francesco was also super communicative and friendly before and during my stay!