Ok,you want the real skinny on this .your going to get it.
Ford has the buterfly valve in these truck to be used for warm up application only keep this in mind cause as a warmup valve there is no pressure to speak of during the idle function.not designed for use as a exhaust brake and therefore has it's limitations as far as longevity is concerned in the bushings and the actual valve itself.Once these parts ware and they will you will need to replace the valve assembly and that can only be done by buying the entire turbo unit itself.Ford no longer sells the butterfly as a separete unit because of this brake.
Now,as for the brake u purchased working capabilities: Yes it will work ,but not well for loads in excess of 5000lbs. The brake will not activate for about 3 seconds after you actually lift your foot of accelerator,and then will hold lockup of the convertor only after you push overdrive buttom off.I don't know about you but when I want my Brake to work i want it now!!! Not when Im already in the guys trunk.There is a hole drilled in the buterrfly to control back pressure and as long as all is functioning right ,this should not allow enough back pressure to build to float the valves.
Hope this explains how they work for you and makes you aware of the limitations of this type of product.
PS. the company that designed that unit is no longer in existance so it's buyer beware.
BD does offer a simular unit that would do nothing different ,just be warranteed.We also offer a complete line of exhaust brakes that are designed to handel these higher weights.They are really what you should consider if you want to protect your investment and have true braking ability.