I don't know the exact amount. What I do know is that they do your instrument rating in a multi. That certainly increases your multi time. Also, what you must remember is because instrument students are in multi airplanes, you will also build more multi time as an MEI (much more). At DCA, you need to be a VERY senior instructor to get MEI time.
Another GREAT thing I loved about flight safety was how they were encouraging their students to instruct. If you stay with Flight Safety until you have instructed for 800hrs (until around 1000TT, where you can start interviewing at regionals), Flight Safety will reimburse you for the cost of your CFII and MEI (thousands and thousands of dollars). That is a nice perk.
If money is no object, then Flight Safety is truly a good and reputable school. However, you are essentially paying $20 more an hour for the SAME airplanes and the SAME instructors you get down the street. Then you get paid $20 an hour less as a CFI for doing the SAME instruction you would down the street. Multiply by 200+hrs (flight time), 300+ hrs (with instructor), and 700+ hrs (as CFI), you are talking about $25,000 more for the same training. But then again, it is your money. Let your conscience be your guide.