Dual camera setup advice

I am using this eRapta backup camera kit. It comes with one display, two side mount cameras and two forward/back cameras. I've not used the two side cameras. The screen allows you to select any of the four cameras or combine them (in various fashions). I'm sure it is not the highest quality option but it is doing an acceptable job for me.

Edit: Maybe worth noting. I recently mounted one of the cameras to my roof so I could see how close I am to tree branches and such. It is not a perfect solution but better than crossing my fingers and hoping! This is not a good photo but it gives you the idea.