I have to agree with others - the OEM fiber drive plates are great. But the aftermarket will function well, too.
On my 89 250, the aluminum driven plates wore out quick. I replaced them with a EBC dirt digger clutch set that had steel driven plates. This will increase durability many times over and give a little bit of the effect of a flywheel weight. It is not attached directly to the crank and spins at different rpm from the crank, so it is not quite the full effect.
Motocrossers use aluminum plates to keep drivetrain weight to a minimum. Similar to aluminum sprockets, lightweight standard chains, etc. This sacrifices durability for maximum horsepower transfer and throttle response.
Functionally, the EBC plates don't have the quality control that the OEM plates have, i.e. flatness and dimensional tolerance. This causes a bit of clutch drag on the EBC until you break it in. In my experience, the OEM replacement never had the clutch drag effects after installation.
Tip: always soak the fiber drive plates in tranny fluid before installing - I normally soaked overnight. You will find that the plates will fit quite nicely inside of an old steel style coffee can.
