I used to work parking brakes. I spent 12 years designing them
To be federally compliant a car has a hydraulic brake system and must have a separate mechanical parking brake. One that does not rely on the same brake hydraulics for the base braking system.
You guys can install those line lock brakes on there but they use the same hydraulics and thus would not be legal and may not pass inspection.
One thing I read was mentioned about hot brakes and losing clamping force. The clamp force does not change. What actually changes is the coefficient of friction between the brake pad and the rotor as the rotors cool. I ran a test years ago where we heated up the brakes on a performance car to 400C and parked it on the test hill and waited for the brakes to cool. Time, temp and loads were recorded when the car began to roll down the hill. The loads didn't change but the friction did as the brakes cooled. Now this condition would only be a concern on a car with an integral park brake (your service pads are also your parking pads).
Those separate systems liket he Ultima uses with a separate park brake caliper allows a higher coefficient of friction pad material and since it is not used for vehicle braking, would be less succeptible to the cooling phenomenon mentioned above.