A fantastic apartment in a fantastic location. I've stayed there twice now and both times the service has been calm, friendly and efficient. The apartment is light and airy with great views over the Tiber. It's right in the heart of the old town, just 5' from the Campo De Fiori and you can walk to pretty much everywhere that matters in less than half an hour. Federico's guide to local restaurants is helpful and - so far - completely accurate!
It is two floors up a fairly narrow stone staircase, so if you have a lot of luggage you might need to arrange help. I've also seen reviews which say it can be a bit noisy but it has never bothered me. Close the shutters on the river side when you go to sleep. A five-star stay!