We had a great time at Carolina and David's place. Communication was fast and easy and they were very accommodating (they let us check in early because our flight got in very early and we didn't want to drag our luggage around DC).
The location was great. The apartment is easy to find and the check in instructions are very clear. There are a lot of coffee shops, restaurants, and fitness studios around the apartment. It took us around 25-30 minutes to walk to the National Mall area.
The bed was very comfortable and we especially loved the bathroom and the nice shower. The TV service did cut in and out quite a bit, but this isn't a problem if you don't plan on watching a lot of TV during your stay. We would definitely stay here again.