Sega controllers have four round buttons and two thumb triggers. This is completely unacceptable for fighting games, where you might have to hold down two or three buttons at the same time to pull off special moves. Trying to do so on a Sega controller is next to impossible. However, most third party controllers have six round buttons (two of the buttons mimicking the thumb trigger signals) as well as the conventional thumb triggers in place. Of course, the best way to play fighting games is to get an arcade stick, but if you can't afford one, a third party controller with six round buttons is the next best thing. Sega controllers totally suck.
As for third party controllers "blowing up the Dreamcast" yeah right.