Pros:
The location is amazing. It's an extremely short walk to the Borough Underground Station. The area feels like a city neighborhood and seems reasonable safe. The building itself seems very secure, and even though we had the windows open at night, it was pretty quite. Although the refrigerator had a strong food odor, it was very useful to have one. The apartment overall was clean, even though it's MUCH shabbier than the pictures lead you to believe. There is two separate rooms...the main room and the bedroom. While the bedroom door doesn't shut, the hallway door does. This was great for us as we have a snorer in the family :)
There is a small grocery store at the bottom level of the building which proved very useful several times. There is also a Starbucks for your morning coffee extremely close by, and one Subway stop away is Bourough Market which is a very large, very cool farmer's market with everything under the sun. But you should know that it's only open on the weekdays from 10-5.
Lastly, our host was very responsive, and answered all of my questions before our trip, which was very helpful.
Cons:
Don't think of this room as a respite from the city. It's a crash pad. If that's all you need, you'll be very happy. Also, even though there's a pull-out sofa bed, it's only useful for one adult who can sleep though anything, or perhaps two small children. The mattress is about two inches thick, and the whole thing sinks in the center. Like...a lot. The white blanket we were provided with for the pull out bed was stained so much that we didn't want to use it. We didn't need to however as it was quite warm in the unit, and was hard to cool off, even with the windows open.
Also, don't expect the washing machine to work. We were not provided with a manual, but we were able to download one online. Even with that, we couldn't get it to dry our clothes. I'm pretty sure it was broken. Other odd things that should be fixed, include the handle to the window that was about to fall off, and the fact that you can't close the bedroom door due to a dresser that is in the way.
All in all, if we were to go to London again I'd spend the same amount of money on a nicely furnished hotel. The big reason we wanted a b&b was for a refrigerator and a washing machine. Well, the washing machine didn't work, and I think I'd trade a refrigerator for a nicer place to stay in for a week with my family.