Everything you've been told so far is true, and goes together.
You want a momentum/accelerometer based brake controller.
The controller does not activate from the exhaust brake. It gets the signal to activate from the brake light switch attached to the brake pedal. When you push the brake pedal, it starts sensing the deceleration and applies the brakes proportionately.
The Tekonsha Prodigy controllers, either P2 or P3, are excellent accelerometer based brake controllers. I've had a P2 for 9 years now. Never felt the need to upgrade.
Imagine if the brake controller started applying the trailer brakes any time you decelerated... They'd be burned up on the first trip!
