They're pretty ubiquitous here in Hong Kong too. As much for protection against scams than actual accidents (i.e. other vehicles and pedestrians falsely claiming you hit them).
>I suspect we'd find a pleasant second-order benefit as well: humans might simply drive better if they know they're being recorded.
If only:
[1] https://www.youtube.com/watch?v=GUoSq8KTzJw (HK crash compilation)