Nice thing about the factory one is that it ties into the factory anti-trailer sway system to actuate the trucks brakes. It is also proportional the the truck brakes, which is something you don't have with the aftermarket units. The last one I had that was proportional was one of those big white metal cased units that actually tied into the truck brake line.
I did some long distance towing on mnine hauling a 7600lb ram 2500HD and it worked flawlessly. I got mine through Temecula Dodge in Kalifornia via ebay, installed it and then had the dealer flash the computer during the next service visit. I'll see if I can find the link and post it.
Edit; Temecula isn't showing one right now but there are several on ebay. Here's a link to one;
A key point is to make sure you have the two plugs under the dash and that the controller comes with the trim bezel.