I'll throw the BD Exhust brake into the reccomended mix.
Haven't had it for long, but it worked flawlessly on the first long trip and provided enough braking power to not use the service brakes on 7% grades, grossing 17-18klbs truck and trailer.
I can tell how well it worked as the brake dust build up after days of mtn driving, over 1700miles, mostly up and down hills. No more brake dust than a normal week or 2 around town, where previously my wheels would have been black after a trip like this.