Well, it’s normal that you see both cameras resolution change in that view, because the addon is pretty much a hack The resolution is a render setting that is saved at a scene level, so you can’t technically have two different render resolutions at the same time.
What the addon does is that it saves a camera resolution per camera, and if that camera is active, then it applies that camera resolution to the scene render resolution.
The important thing here is that you can’t have more than 1 active camera per scene in Blender. If you set different resolutions in your cameras, and then switch the active camera, you will see your render resolution update to the camera resolution.
I’ll look into the 2.79b issue!