If towing a vehicle without secondary braking is unlawful, then I would think LEO's in every state would be funding their agencies by issuing tickets to every vehicle being towed from the USA into Mexico. Piles & piles of vehicles get towed to Mexico using those $30 disposable tow bars sold at auto part stores. Just ask a store that sells those cheap bars.
With that said, we used to tow without secondary braking, a 2100 pound car, a Toyota MR2 Spyder. It was amazing how that little car would push on the motor home while braking. Later we replaced the car with a 2006 Jeep Liberty 4x4 with secondary braking system called Unified by US Gear. Since, we actually stop sooner than if towing nothing. When the sensitivity is set so, the tow vehicle helps slow down the motor home.
With that revelation, when the Jeep needed brakes, I installed drilled & slotted rotors and ceramic pads, for better braking performance, just to benefit towing.
