If I ever buy such an "auxiliary braking system", it will be the Ready Brute or Ready Brake system from NSA.
The Ready Brute is a complete towing system; towbar, braking system, etc. ready to install.
The Ready Brake is a ball mount and cable to be used with any towbar.
Both system,s are simple, mechanical, relatively easy to install, and there have been few reports of failures.
No electronics to short out, no compressors to wear out, no heavy boxes to wrestle with, just a simple mechanical surge brake system that works.
Very few states have a law requiring an auxiliary braking system on towed passenger vehicles.
