We had a Brake Buddy for years. We had 2 problems:
1) small split in the plastic air hose at one end. Easy fix.
2) Twice an internal bolt came loose--we thought the compressor had died, but it was just the bolt that connects the piston to the motor had fallen off. Again, an easy fix.
The unit comes apart and reassembles quite easily.
We were quite happy with it but now tow a 4 jeep and now also have a DP with air brakes so now we use Roadmasters Invisibrake which operates directly from the DP's air brake system.