The dual dash cam is worth it in my opinion. Just the other day someone ran into the back of one of my vehicles. I have a great video of them not looking ahead, their shock at the impact, then fleeing the scene of the accident. Video on its way to the police.
Some guy rear-ended Mrs. Q. I told her to call the police who promptly arrived at the scene of the accident. The driver who hit her claimed that the damage to her rear bumper was pre-existing, and the police supported him...until I arrived and suggested that the officer go back to Sherlock Holmes University because there was a clear imprint of the guy's license plate in Mrs. Q's bumper.
I'm surprised they caved so easily. Over here they'd have made you exchange details in any event, in fact it's an offence over here not to provide details.
Something worth remembering, even a forward facing camera with audio will record the sound of a rear impact and probably the jolt visually as well. Very useful to remember if the other guy claims not to have hit you.