The single master is perfectly adequate and was used by most all cars and trucks well into the muscle-car era. Our trucks have what was then called an "emergency brake" a cable operated back-up system (now called a parking brake) and from what I've read here and elsewhere works a whole lot better than 1/2 of a dual system in an emergency. I've been driving single systems for longer than I want to admit and never had a failure. Keep them adjusted and periodically inspect everything, you'll be good to go IMHO.
