What a wonderful experience! The apartment is small, clean and efficient. The location was perfect for us - within walking distance of all major tourist areas and Trastevere itself is full of charm and character. But the best part was meeting Gianluca and Laura. They were quintessential hosts; warm, engaging and happy to help in any way possible. When our luggage was delayed, Gianluca volunteered to have it delivered to his shop, so we wouldn't have to wait around all day for the delivery service to arrive. Laura took extra time to make sure we had everything we needed and to make suggestions for dining, shopping and local sightseeing. They are proud of their community and it shows.

Observations for future travelers:
This apartment is perfect for 2, but not many more. A/C was a godsend (temperature during the day was 40 or so).
Plenty of eateries nearby.
TIM SIM card for mobile was worth the price. We communicated regularly with Laura by txt.
Laura arranged a ride from FCO to the apartment and back. It was 45euros and well worth it. There is no direct public transportation to this area.
We spent little time in the apartment, except when we slept. There's too much to see during the day and just sitting outside at one of the many cafes is so pleasant, you want to be out all the time.

Recommendation: Rent this apartment, because it's a great location; it's clean and comfortable; and if for no other reason - you get to meet Laura and Gianluca.