I've stayed just one night at Chiara's house and it was perfect! The flat is just like in the photos. It was really clean and organized. She was kind and flexible about the arriving/departure time.
If you're coming to the EXPO, it's a great place, cause you can catch a train in front of the house that will leave you in the door of the EXPO.
If not, even if you're a bit far away from Milan's downtown, it worth it. 'Cause she is so nice and will help you if need!