Vented flywheels cool the clutch bell, more than the engine (although they probably do cool the engine a little bit). Usually, they are a little lighter as well, which in theory provides slightly better engine response, but in reality they don't make a very big difference. If you're one of those people whose clutch bell gets discoloured from the heat, then it's probably worth doing, otherwise, probably not. It seems that the pros don't really bother with them. They are nice and bling tho'...