The short version: if you are still in doubt, don't be: just book this place! I highly recommend staying at this beautiful appartment.
The appartment is perfectly located just 100m away from the beautiful central town square in the old city, but in a very quiet street. There is no better location imaginable. Despite being in the small streets of the old town, we got excellent help to reach the place by car to drop of the luggage, and to have a secure place to leave the car in the old town during our stay. All communication was extremely easy and friendly. The apparment itself is very charming. Despite having all the charm of staying in the old town, the place is renovated with all modern comfort. The rooms are large, clean, and light. There is airconditioning (although we didn't need it), and a place to stay. The bathrooms are large, clean, and very new.
We had a wonderful stay and I would definitively recommend this place, and hope to return if we are in Bergamo again.