Guest: I have a 5200i flash that is 15 years old. It will fire on the 7D but can effectively only be used on M mode. This is no good for "fast action" images where you must ave fast exposure controls. However, if you have time it works reasonably well. Two weeks ago, I used the 5200i on the 7D at an anniversary party. For controlled shooting it was fine. The speed was set at 1/60 or 1/125 and all I had to do was change the aperture between 5.6 and 11 (as I recall) depending on distance. I took lots of shots of people speaking from a podium, so distances were within a narrow range. I had time to take several images anyway, so could make minor adjustments in aperture to get the correct exposures.
I used the 5200i two weeks ago to take closeup "studio" shots of barley seeds. Using the flash's exposure ratio controller and a white foam diffuser, it worked well.
My 7D came with a 2500 flash and it is useless. Why they shipped it with the camera I'll never know. I am trying to get a credit from the Canadian agent for KM. If they cooperate, I will perhaps get a new digital compatible 3600 flash.