Overall, this apartment worked out well for our family of five. The location in Monti is excellent. It is a short, three-minute walk to the Cavour metro station which is one short stop away from the main Termini train station. It is about a 10-minute walk to the Colosseum. There is a grocery store nearby (Elite) that is a 5-minute walk.
It is in an older building, so be prepared to deal with some of those issues. Specifically, it is on the fourth floor and there is no elevator in the building (that is a lot of stairs when you have a large piece of luggage with you). We had issues with the lock on the building door while we were there (we were effectively stuck in the apartment for a few hours because we didn't have a way to re-enter if we exited the building). Also, the tenant below complained to us that our footsteps were too loud during the night. Our only activity during the night was getting up to use the bathroom, so obviously the floors don't do much to contain the sound. There are a couple of potentially dangerous, unexpected short steps (3 to 4 inches) in each of the bathrooms (definitely not a unit that I would recommend for an older person that would be more likely to fall) -- for us this created a couple of near falls going to the bathroom in the middle of the night.
The unit itself has been redone somewhat recently, but it still has the feel of an old apartment building. We never did figure out how to use the oven (and our check-in person was not able to tell us how the oven worked, fortunately there was an additional toaster-sized oven in the unit). The refrigerator seemed new, but the light strobed on and off when the door was open (and this was not fixed during our 4 day stay).
The host was okay, but not as good as other AirBnb hosts that we have experienced. He arranged for a ride from the airport, but that ride never showed up forcing us to scramble for a taxi / limo that could accommodate our family of five and all of our luggage (and that cost more than we expected). Our stay was in December. The heat to the unit was turned off when we arrived and it was VERY cold. It took about 90 minutes for the unit to warm up. After arriving at the apartment, we reported several issues. Some of the issues were addressed (e.g. there was no soap, towels for the kitchen area), but other requests were just ignored. The most significant request that was ignored was the request for an additional set of keys. We were supplied with one set of keys which was not ideal for our family of five people. To the host's credit, he did reply very promptly when we ran into issues with the lock on the front door of the building (he helped deal with that problem very expeditiously).
Overall, the value for this apartment seemed "okay", but not great. If your primary decision point is location then this is a good choice. If you are more concerned about the quality of the apartment itself then you can probably find other places that are a better value.