Why on Earth would a circular saw on a RAIL need a riving knife for kickback protection? Especially when it's primarily used on panel products which, by nature, don't get the urge to close up like improperly dried hardwood lumber might.
I haven't yet used one (plugged in) so I can't tell you from experience. But if you're hanging the motor off the edge of the rail, I'd think you'd want both clamps for the rail and a catch on the saw to keep it more steady.
-- Know how to listen, and you will profit even from those who talk badly. -- Plutarch