The cabin camera are pretty much just the cabin, some times lighting will even make the outside you can see very overexposed.
A front and rear camera is all you need if you are not doing uber stuff on the side, and even then most of what you need will probably be captured on the front camera.
You have to remember the front camera always log your driving, and if that is within the law then what ever happen off camera cant really be your fault.
So the phone junkie that take you out from behind on a highway, and him and his 2 friends in the car claiming you changed lane right in front of them, well your front camera will have you driving nice and easy in your lane right until BAM !
So clearly they are lying in the other car, and you dont really need the footage from a rear camera to prove that.
Though i do still recommend people to get a 2 channel system if money allow for it, but in my 10 years of dashcam use and uploading to youtube, well it is just B-roll footage i get from my rear or side cameras, the action are pretty much always on the front camera.
And thats how you should look at dashcams, as a means to document your driving and actions, and pretty much any dashcam will do that 100 % no matter the weather or time of day.
Then on the side you will capture a lot of other stuff, maybe even the plate of the guy that hit and run on you, but due to limitations in dashcam technology used ATM thats far from certain.
Americans need 2 dashcams as often cars only have 1 plate ( on the back ) so a front camera will capture nothing much of a oncoming offender, but your rear camera might get lucky as he speed away.
We Euro boys are more lucky, cars here must have 2 plates and they are a bit larger and more easy to read so we have 2 X the chance of a plate capture VS a American.
Front and Rear cameras on the A139 in my car on a day with very marginal conditions for plate capture, 80 Km/h - 55 MPH speed.