I can only say positive things about this place.
The apartment is lovely and literally a 5-minute walk from the Pantheon. This means if you are primarily interested in the main attractions (Vatican, Colosseum, Spanish steps,...) you can reach everything on foot and don't even need public transportation (which also gives you the possibility to explore all the nice small streets in Rome).
If you are very large (upwards of 2m) you this place might not be entirely for you since in particular the bathroom has a very low ceiling so you might be a little uncomfortable (though it is entirely possible that this is the standard in Italy and you will not be more comfortable elsewhere either).
Communication with Carlo (or rather his son Alessandro) was phenomenal. He was very quick to respond to any question and we got a detailed message with some great restaurant tips, some of which we tried and were very pleased with.
Sadly we had to leave a day early, due to a cancelled flight; we would have loved to spend even more time there.
I can only highly recommend this place