Positive: The place is very nicely located, it is easy to reach from both airport and the main train station, the restauraunt district in 3 mins walking is amazing. The flat is very romantic in terms of the real "Rome with wooden sealing" wibe. If you plan 2-3 nights in Rome - the place would be a nice choice. But if more..
Negative: The hot water in the evening is enough exactly for one person, the next one will have to shower with cold water. We were in Rome in March, so we needed a heater. The heater is VERY old and VERY loud, so we were not able to sleep when it was on. If you want to stay in Rome in winter, you might need to consider another place. Also the windows have no isolation whatsoever, so you feel like sleeping right by the people shouting in the bar downstairs.
In general, I would recommend this flat for max.2 people in late spring to early autumn for 2-3 days.