Well since you are looking for input, and I know this is counter to what others have said, here is my 2 cents...
As background, I have only owned Diesel trucks and tow 15-20K miles per year. I am also 23 years in the fire service driving large, heavy (50-70K lbs), firetrucks. Real heavy duty motors, trans, frames, etc. Some with exhaust breaks, others without. Those with exhaust brakes are driven almost exclusively with the exhaust brake disabled.
... a reminder, this is my opinion and may difer from others...
A little 3/4 or 1 ton pickup with a 14-18K 5th wheel in tow does not need an exhaust brake. If your truck cannot stop your 5th quickly and safely, I would focus on upgrading the truck brakes. Even with the Monty brakes disconnected, you should be able to stop the Monty safely, although hopefully you will never need to do this except in an emergency situation. If your Monty cannot stop itself, I would get the brakes fixed/adjusted. (When I say, Monty stopping itself, this means, correctly adjusted and maintained, you should be using similar or maybe slightly more braking force while towing than you do not towing. If you feel like the Monty requires a lot more braking effort from the TV, you may want to get the Monty's brakes fixed/adjusted. The Monty should not be pushing the tow vehicle. I know it is heavy and all, but remember, you are towing/pulling the 5th, it should never be pushing you... even when stopping. A trailer pushing a tow vehicle is also known as a future jacknife.) And forget about using the exhaust brake to save the pads. Change them every season if you do a lot of trailering, it is cheap insurance. On long grades, lower the gears and let the engine and transmission hold you back to prevent overheating the pads.
It's not that I don't believe there is a place for an exhaust brake... Real Heavy Duty Trucks with an integrated exhaust brake designed in that are used to transport heavy 50-80K loads sure. They are also designed with air brake systems. The key here is, 'designed into the system'. In most cases, they still rely on the lower gear to slow on long grades...
Exhaust brakes, like air brakes, just don't belong is light duty trucks. Adding a new braking feature, not designed into the overall truck system is... what lawyers hope for after an accident where the driver may have very well be 100% not at fault. Maybe I've been at too many accident investigations in my line of work and become a bit over sensitive to after market mods. All I know is when an accident happens, the lawyers head for the party with the deep pockets. Let them go after Ford, Keystone, Firestone, etc. Don't give these big guys an out by changing your braking system...
Anyway, my 2 cents... of course it's you TV and money and you should do what you feel comfortable with. Good luck with what ever decision you make. Tim