Hello
I recently picked up mint iSight camera. No issues. No Problems. Runs great on my 2012 mac mini. I already had a FW 400 to 800 adapter (RocketFish) so that came in handy, since my 2012 has only a FW800 port. http://www.amazon.com/Rocketfish-Mac-FireWire-Cable-adapter/dp/B005JL2PXA
I plugged the FW400 adapter end directly into the iSight and ran FW800 cable from the bottom end of the adapter the mini's 800 port.
FYI .....Actually the 800 cable snaked in through the iSight laptop monitor adapter pretty nicely (where the original apple FW 400 cable was originally), and then I plugged the 800 cable into the bottom of the RocketFish, and then plunged in the 400 end of the RocketFish, directly into the iSight. If that makes sense.
I can confirm that the iSight works under El Capitan, and as a precious poster said......"works in FaceTime, iMovie, and Quicktime".
My one suggestion with audio, in El Capitan, be sure to go to System Preferences>Sound>the Input Tab, choose iSight (it should be listed there). There is actually a display setting that shows you in real time the volume level of your input from the camera.
Hope this helps someone.
Regards