Mario is a great host. Quick responses to questions. He accommodates requests. The apartment has a fantastic location, with many, great restaurants within a minute's walk and easy access to sites and public transportation. The apartment is also very clean and has a washer/dryer, which makes longer stays easier.
Just be aware, the downside to such a well located apartment is that it can get a bit noisy with crowds outside at night (that said, ear plugs can easily fix this, or you just stay up later).
I wouldn't hesitate to book this apartment again if I return to Rome.