I use the ones from blackboxmycar.com. Very good quality.
Really only used it once, to validate I was not hallucinating. Was in SC on the way back to GA and it was about 10pm. Came around a winding corner on the interstate and damn near killed some woman who thought it was wise to walk across the interstate. It was so shocking, I was like, WTF was that... Did I imagine that?
Reviewed the video and there she was. I was going about 75mph if I recall correctly and she was walking so fast that she damn near hit my side mirror. Scared the hell out of me.
There are many times, where some asshat does something that makes me say outloud, glad I have cameras in case this goes bad...