There have been some good comparisons posted but I don't know offhand how to find them. Perhaps somebody else can post a link. My takeaway was that the dual lens camera is better in low light. The downside is that there's an unavoidable parallax issue with the separate lenses, resulting in a distance where the 2 images converge. This distance is somewhat close in (sorry I don't remember the number in feet). The bottom line is for close-in details like face recognition, the dual lens is the choice. For further out distances, the 4K-X is better. My application was for a large area overview, so I chose the 4K-X. Some discussion at posts 145 and `157 in this thread Worlds First Review - Dahua DH-IPC-HFW5449T1-ASE+D2 - Dual Lens Full Color 2.0
If I am not mistaken there is camera that has one lens and two sensors. A dark sensor and a light sensor. It then uses the best of both to make a single image.
I'm not aware of this configuration and need to learn of it if it's real. I can't help much with info on the 4K-X because so far I only set it up temporarily for a few days, and have to wait for the ground to thaw to run my cat6 a few hundred feet from the house. I can confirm that its low light sensitivity is a clear upgrade from the 5542 series, and it gives a viewable image with only moonlight. By viewable I mean you would be able to see people or animals passing by. The moonlight-only picture is a bit grainy, and IVS line crossing didn't trigger. Wildcat_1's reviews are the main source of my 4K-X knowledge.