Marco's place is right in the heart of Rome near much of what you'd like to see while you're there. The Vatican is ~20 min walk, Pantheon about ~8 min walk, Tevi Fountain about ~15 min walk and even the Colosseum isn't too far.

The place is high up and there are 4 steep flights of stairs you need to climb to get to the place, so if you have physical trouble or don't want to deal with the trek up to the apartment, I wouldn't recommend Marco's place. I was there in August and it also gets quite hot in the upper room (the lower floor stays very cool with AC on).

However, if you're looking for an affordable, clean place close to everything you'd want to see in Rome, then I can't recommend Marco's place more highly. They were very communicative and made it easy to enjoy our trip and there's a ton of great food/restaurants nearby to enjoy.