I've recently fitted a small camera that sits behind the rear view mirror, I was not offered any discount from my insurance company upon the recent renewal. The camera is easily detachable and records excellent footage of the road ahead. We fit the camera when towing or travelling away from home, it's not there to gain a discount on our insurance, it's just there to create a record of any incident should the need arise. We don't use it locally as we don't think it is a good idea to leave it in the car visible to anybody who may wish to steal it.
some of the large insurance companies and brokers supply them to the haulage industry to get the premiums lower price. the last new tipper we bought came with 5 cameras and a recorder fitted that runs all the time the truck is running.the driver has no control of this.