Francos Flat is beautiful! It's very central and we did everything by foot (from colosseum (10min) to castel st angelo (1 hour)). Franco was nice and recommended restaurants and gave tips about pickpockets.
Leaving our suitcases in the flat longer than it was planned was no problem for Franco and was perfect for us!
The via merulana is very central, which makes it also very loud (many cars and scooters and honking all the time!) It was okay for us, since it was only three nights anyway and Franco has a big heavy curtain in front of the door which blocks a bit of the noise :)