The location is really the best thing about this apartment by far. My boyfriend and I were in rome for 3 days and walked literally everywhere except to the airport. Vatican city, forum, palantine hill, central station, national museum, etc etc all very close (1 hr walk at the very most but there are usually things to see along the way so it doesn't feel like you're walking through nothing for an hour to your destination). We found Rome to be generally very walkable!
Check-in was smooth, wifi was decent, really nice to have the shared coffee machine and washer/dryer outside the apartment (all for free).
Our main complaints were the noise level and the lights in the apartment. To start with the lights, they don't have any shades on them and were way too bright!! It was uncomfortable to have them on. And unfortunately even in the daytime the small window is not enough to sufficiently light the apartment. This problem is of course easily fixed by adding some lampshades or changing the fixtures, so it may be different when you decide to stay.
The noise level was very hard to bear though, and this is something that i don't know if it can be changed. On the first night, I think the upstairs neighbors were having friends over or something and it was impossible to sleep. It was loud enough when they were walking around, but then to have people over on top of that was REALLY loud. Because the bed is so close to the ceiling I think it magnifies the problem. And you can also hear happenings at the front door as if they are right next by.
That being said, while the first night was pretty miserable due to the noise, we went to a pharmacy the next day and paid 5 euros for 2 pairs of earplugs that we used the next two nights and slept in total peace. So my advice to you would be to book the apartment, it is a great center for exploring rome and very cosy. It is great value for the location and amenities. But bring ear plugs, and hopefully the lights have shades by the time you arrive :)