How much aux brake effect should I be sensing?

If everything is working correctly you should feel nothing. The braking system should only compensate for the weight of the towed vehicle. The only way I know the brakes are active is when my dash indicator comes on.

I drove a block with the toad parking brake set and the only way I knew something was wrong was that my continuous fuel mileage dropped below what I normally see pulling away from the curb. Felt nothing both accelerating and braking.