This is an amazing place to stay - cozy, as described, and at a perfect location: Back Bay is great. Newbury street is wonderful and has many shopping/dining opportunities. Ideal for leisure trips as right next to some of Boston's best shops and very well connected to other areas of the city. Also great for those visiting for work at Boston University etc. Sounds of life from Newbury street make it into the appartment (you're 2 floors above street level), but I'm a light sleeper and did not find this bothersome at all.
The place itself is comfortable and well-equipped and while it is small it's not cramped or claustrophobic. Easy to get in and out of and the hosts are very nice and responsive to communication.