My eldest had a black box in the car.
The first time it was driven, we looked at the app and it was completely random. It looked like she had driven through a prison and gone around a play park.
I told her to contact them immediately so that they have it on record that the data isn't to be trusted, which she did.
Basically, if it works properly, once they reach a certain number of 'penalty' points their insurance is likely to be impacted in some way or premium goes up etc.
Could be emergency stops (which is sometimes quite a bad thing to penalise), or sharp cornering, or starting from a stop too quickly.
Seems any excuse.
Try and imagine putting a full glass of water on your head whilst driving. That ended up taking the safety aspect to such an extreme it became the aim not to upset the glass of water rather than the secondary mission of avoiding the child running out into the road.
Also, they sometimes charge for one to be put on, and more importantly, to be taken off afterwards. Luckily our one was just a couple of crocodile clips but with the proviso that if it wasn't connected (for any reason), she wasn't insured.
Luckily she is a careful driver anyway (now a blue light person as a passenger as she is too short to reach the pedals properly so can't drive the vehicles)