We have the ready brute elite which includes the ready brake integrated into the tow bars. It was installed a year ago and we have driven 18000 miles with the jeep attached since then. We have had no problems whatsoever. We have traveled up and down mountains (up to 12% grades) on gravel and dirt roads, camped on the beach in sand, been through rain storms...just about any condition you can think of.
The brakes on our jeep are fine - no unusual wear at all. There isn't constant braking - it should be the same as using any other braking system. And no, going downhill with a ready brake system does not engage the brake. We don't have to worry about plugging the brake system into the jeep - the ready brake requires no electrical connection.
I'm not sure of what salt corrosion your dealer is referring to but we have had ours caked with pounds of Dalton Highway mud and... nothing happened. We washed it off and the brake works fine. There is some wear on the external cable from rubbing but we figure another few thousand miles and we will replace the external cable just as a matter of course. It will take all of three minutes and cost maybe $15 for the cable and hooks. All the parts on the brake are mechanical - mechanical parts are pretty easily replaced.
We are extremely happy with ours and would buy one again.