I have the 4" BD w/airpump, and TowLoc installed. Very happy with the unit. We did the install, the E-Brake went in easy, but the TowLoc Box took some time to wire into the harnest. (Wished the TowLoc was Plug & Play). I looked at all the E-Brake system, I was impressed with the BD setup and the option to Fine Tune the TowLoc with my Laptop. I haven't found a downside of the unit, other than the TowLoc install. I go up and down Cajon Pass just about every other weekend with our 5th wheel. My BD does an AWESOME job holding back my truck and trailer going down the grade before the Run Away Truck Ramp and, before the 15/215 Jct.