Kelly's place is in a great location in Columbia Heights, about a ten minute walk from the metro station. There was a useful book of suggestions for things to do in the area, and important information about the flat. It's also a little under an hour to walk down to the mall, and half an hour or so to various other interesting neighbourhoods. The aircon is fully functional too, which was really important for DC in summer!
Checking in/out was perfectly simple - we could turn up basically whenever and let ourselves in, and then we locked up and left the key in the lockbox when we left. There were two sets of keys, which was definitely useful - we were two couples staying in the same flat, so it was good to be able to head out and not have to worry about the others getting locked out.
The flat has all the amenities - we especially appreciated how there was laundry powder, good bathroom supplies, and some food in the fridge.
One small caveat: we wouldn't recommend it if you're here to work or concentrate, as the footsteps from upstairs can be loud. But as somewhere to have as a base for a holiday, it's pretty much perfect.