I have a B40 (
https://dashcamtalk.com/b40-a118/ ). It has sound, and works quite well. It's easy to install; it comes with a cable and lighter adapter that you can plug into the receptacle behind the glove compartment.
Here's a video of mine with a bus cutting me off at the 1:30 mark: [ame="https://www.youtube.com/watch?v=1mPaauuyShQ"]Durham School Services bus cuts me off. - YouTube[/ame]
Note that the video from the device is much better than that shown; Youtube really compresses the video.