I love staying at this property when I'm visiting Boston! The Beacon Hill location is amazing and I enjoy the flexibility of staying in a mini-apartment rather than a hotel. Maverick's team is very responsive to any questions or issues that come up.
My only caveat re: this unit, along with units 13 and 14, is one others have already mentioned: it's a fourth-floor walkup, and the third flight of stairs in particular is pretty steep. There is no elevator and no way to get your luggage upstairs (or downstairs) other than carrying it yourself. If that presents a problem for you, I suggest opting for one of the lower-floor units if available.
Also, if you're tall or there's more than one of you traveling, you may want to pick another unit as well, as this one is under the eaves of the roof and has a slanted ceiling. As a solo traveler who's barely 5'6", I was perfectly comfortable.