First and clearly one is to see from the appearance, there have two lenses set in together and work together, like the “AllCall Bro” combines dual lenses with two separate sensors, 8.0MP main camera captures static images while the 2.0MP subsidiary captures depth information.
Secondly, the smart phone have dual camera have better effect in photo contrast, photo brightness than single camera, maybe you can make a comparison with dual and single camera phone.
Third, take photos in poor light, hide the main camera with a object like paper. If you can get a picture have black and white images or a picture with blurry scene, this is a true dual camera. If you get a image with nothing, the Dual camera just is gimmicky.
Fourth, in preview mode, you can select the focus and adjust the degree of blur. Let you to take SLR effect photos with smartphone.
So, by now I believe you have a deeper understanding about the Dual Camera, “AllCall Bro” as a latest dual camera high performance Smartphone may beyond our expectation.