You can argue redundancy with 2 single cameras, and that is also true.
BUT ! say your front camera go bust or dont record, then the rear camera footage might not be worth much depending on what happen and how, and vise versa.
On the other hand the single memory card in a dual channel camera can take out both cameras if that go bust, in which case you have nothing at all.
Still i would take a dual channel any day over 2 single, not least if i have 0 to start with, if you already have one, then adding another single are a option.
But i would not have a "huge" SGGCX2 on my rear window as it at least have a 2 X large footprint compared to the DC rear camera.
I am not sure if the hardware dual channels cameras are based on have better options for warning of non recording camera, that i know at least on "old" hardware could be a problem as a camera would appear to be recording judging by visual things like LED and LCD screen, but in truth the camera stopped recording long ago.
Error warning i think are a big must have in cameras nowadays, not least since many actually do think the dashcam are a install and forget item, and sadly thats still not true with any hardware.