The EZ Brakes system seems to be self contained where it has its own battery and uses the brake lights to activate. It has its own brake controller, probably time based. It sounds like a good system except that without a controller inside the truck, you can't activate them independently from the trucks brakes if the trailer was to sway or skid, although you could lightly touch the brakes to activate them. I guess it will be OK, you just have to be sure the battery is good, that it has a 7 pin round plug (or an adapter) and that you connect the red wire next to the battery under the hood to the positive post at the mega fuse so the battery will charge.
If it ever fails or the battery dies, it would probably be cheaper and better to just get a gravity based controller and install it as per the instructions posted above.
Just my