I stayed at this place with 6 friends, so 7 people in total. There are 4 bedrooms - two with double beds and two with queen beds (I believe it's advertised as 4 queens but I don't think they all are). It's a long narrow apartment and the wifi does not reach to the furthest two bedrooms which was super annoying.
The living area had a couch for 3 people and a random assortment of office type chairs - this was strange for a place with space for max 8 people - definitely not enough seating for everyone. The kitchen was missing key things like oil and salt & pepper. In the kitchen and first one or two bedrooms you can hear the noise quite easily from the next apartment over - the walls are thin.
The location was great! Walkable distance to the Quincy Markey (5 min), Public Market, Back Bay (15 min), and the Park Street station on the red line (subway) was about 200 meters from the front door.
Check in is 5pm and checkout is 10am which I personally think are too late and too early respectively, but we were able to pay $50 USD for later checkout which was appreciated. Brian and Heather replied within the hour during day hours which was awesome and the checkin / checkout instructions were super simple and easy to follow.
Overall I'd recommend staying here, but probably not with more than 5 or 6 people.