Gator,
In the mid 90's when evaluating various braking systems I preformed a simple test. While coming down a straight stretch of mountain road with no traffic, I turned off the engine and applied the brake. After one or two pumps, the residual vacuum was gone and the brake pedal had no effect as hard as I could push on the brake pedal on a 5300 pound vehicle.
This is the basis of most supplemental braking systems. Granted, the box-on-the-floor systems will have much more push (or pull, depending on the system), but how much stress do you want to put on a pedal and it's linkage designed for the average human leg strength.
I opted for an M&G system and found when towing it actually stopped the MH faster because of the four wheel braking of the Bronco added considerably to the really lousy air-over-hydraulic all disk brakes of the Beaver Patriot. When getting ready to travel, I quick connected a coiled air line from MH to towd. That's it. Done. No switches or levers to adjust. No LED's to watch. We now have a bus conversion with much better full air brakes, but still I use the M&G when towing our 6100 pound van.
Two points:
1. Compare costs of systems with and without installation labor. The cost of most box-on-the-floor supplemental braking systems will meet or exceed the M&G system in most cases. And no, I have no relation to M&G other than the fact I appreciate a well engineered and simple system that does not put excessive stresses on portions of your towd that it was not designed to have.
2. ANY supplemental or primary braking system can exhibit problems if it is not installed properly.
The only downside to the M&G system is they do not have cylinders for all cars and trucks. Particularly the smaller ones. My wife's 2300 pound Escort fell into that category due to the compactness within the engine compartment and the fact that model is not highly used as a towd.
So you pay your money and hopefully ride safer.
Chuck & Elva Newman
F162285