Rather than a traditional B&B, Colosseo B&B is instead a group of separate apartments run by a man who is a leatherworker by trade (and operates as shop just a few doors down). So unless you're sharing an apartment with other people, it is a very private, independent experience.
The B&B doesn't offer an English/American-style cooked breakfast -- instead, each apartment has a kitchen that is stocked with an espresso machine, packaged bread, and juice boxes. However, there are several cafes nearby, so it's easy enough to visit one in the morning and get a cappuccino and cornetto before waking down to Rome's sights.
In terms of location, it a short walk from the Colosseum, Roman Forum, Capitoline Hill, and other central sights. Because central Rome is small, it's also easy to walk across the city to Trastevere, Piazza Navona, and even the Spanish Steps. To get to the Vatican, the quickest route is to take the metro from Termini Station (which is about a 10 minute walk from the B&B).
Restaurants in Rome don't start serving dinner until 7 or 7:30pm, so you'll probably want to freshen up, shower, and change clothes between a full day of sightseeing and having a nice meal. The B&B is in Rome's Monti area, and there are a good number of restaurants to the west of Via Cavour along Via Panisperna, Via Urbana, and the other small roads in this neighborhood.
In short, Colosseo B&B isn't luxury accommodations (and there aren't any amenities like room service, a pool, concierge, etc.), but it's a great value in a really convenient location. The apartment we stayed in was small (the bathroom was particularly tiny), but the bed was comfortable, and it was really easy to get to the airport with Termini Station so close by.
My only complaint would be that the neighbors listened to their TV really loudly... and then talked to each other even louder so that they could be heard over the TV. On top of that, they also seemed to have a baby that cried and a dog that barked. But they were quiet enough after about 10pm in the evening, and because our apartment was at the back of the building overlooking an interior courtyard, there was no street noise and no noise from the metro below (though you could feel a slight rumble when the train passed underneath).
Note that on Via Cavour, the odd and even numbers on opposite sides of the street don't match up, so if you're looking for the B&B, make sure you're looking at the side with the even numbers, not the west side with the odd numbers.