brake controllers

Now that direct link, I would trust. As it is sensing brake pressure from the vehicle. Also using the vehicle to sense if the brakes have been applied with no system pressure. Allowing the system to use the trailers brakes if the tow vehicles brakes failed. That is a feature the max brakes and brake smart had. Integration with the vehicles systems is the best solution.
A decilerometer will only apply trailer brakes if it senses a slowing vehicle. Sometimes it could be too sensitive or at other times not sensitive enough, as road conditions change.
A integrated controller takes care of that issue.