The apartment is brilliantly located near the majority of tourist sites - e.g. 10/15 minute walk west to the Vatican, 10/15 minute walk east to the Forum, and a further 5 minute walk to the Colosseum. There are plenty of shops, restaurants and bars close by and it's a 5 minute walk across the river to Trastevere, which has a lively, friendly atmosphere in the evenings. It is also close to several bus lines which take you to all the sites and Termini train station if you don't fancy walking.
The apartment itself is as described, a double bedroom with a kitchen and bathroom and a functioning air conditioning unit. It isn't the biggest but has everything you need, plus a few nice touches - the kitchen had useful essentials (salt, sugar, pepper, oil, milk, etc.), and there was a bottle of wine with biscuits and small chocolates to welcome us.
As a host Costanza was very quick to respond to any messages with questions we sent her in the weeks preceding our visit, and she greeted us at the apartment. She gave us several useful hints about the best places to eat, local bakeries etc, and also the best ways to see the city and various sites.
Overall we loved our time in Rome and would highly recommend this apartment!