I started with the US Gear system. It worked fine the first year. Then the black box failed in the middle of a trip the next year. US Gear sent me a new one on warranty to a campground I was at. The 4th year, the vacuum pump failed. US Gear wanted $460 for a replacement. I found another (actually from Ready Brake for half that price). That also failed a year later. On hind sight, I should have taken the vacuum pumps off when they weren't needed and kept them somewhere warmer and cleaner than the engine compartment of a vehicle during a Minnesota winter.
Rather than spend more money on the US Gear system and it's electronics, I bought the Ready Brake system (including break-away system) for about $500. It has worked great so far and no electronics to fail in the middle of a trip.