I worked there before the merger with Detica. DFI was a worthwhile experience for anyone starting out in DC. Everyone there works very hard and it was fun to work with a group of such dedicated people. I'm not sure what has happened since the merger and the move to Ballston, but I hope that it hasn't grown too large!
Make sure that you are comfortable with being a consultant. Also, you better have excellent Excel skills - spreadsheets reign supreme!