Every flash unit like that has a trigger circuit that actually fires the main gas discharge tube. In the old flash units of 25 years ago, the trigger circuit had 200-300 volts DC on it, so as the camera's shutter circuit shorts against that, the shutter circuit had to be able to withstand that big voltage. In the newer flash units of the last ten years or so, and like the Canon Speedlites, the trigger circuit has only about 5 volts DC on it, and that is much easier on the camera's shutter circuit. Many modern Canon bodies tolerate only 5-6 volts.
So, you can use old flashes with old cameras, and you can use new Canon flashes with new Canon cameras. When you go mixing old with new, you might possibly burn something up, so there are "safe-sync" devices available to protect cameras, if necessary.
---Bob Gross---