PacBrake does it for me. Thought I would just weigh in on this. Reasons in my decision: 1. ) Not being belt driven means you never have to worry about the tensioner or its bearings or the belt, etc. (By the way, just what does happen when you blow off the belt on the OP's e-brakes when you're on a four mile long, 6% downgrade?) 2. ) The fact that PacBrake only makes exhaust brakes and the owners hold a bunch of patents on them as least says to me that they're 'into' the subject matter of braking. 3. ) My baby Cummins is the smallest e-brake PacBrake makes... they also stop the big ones.
Having said all this, I have never had experience with the OP e-brakes. And
they replaced the firewall mounted air compressor with a new one mounted on top of the engine... (barely audible, now) ... free! (I did agree to buy an air tank from them. )
In short, I'm very happy. Get the on-off button on the shifter. Worth it.