I bought one for $20 to try it out, so the quality is ok in the case of an accident as you will clearly be able to see its the other guys fault.
Quality wise, you can read signs that are close, but licence plates don't show unless I'm directly behind a person at a stoplight.
It would not be useful to record a trip.
After having it for many months, I'm going to buy a better one for the front of the vehicle and put the cheap one facing the back.
I do love that once you have them set up, you can ignore them as they turn on/off automatically and do their job.
About 1.5 yrs ago, a fella pulled out right in front of me and although I braked hard, I hit him. Later his insurance company phoned me without identifying themselves as his insurance company, I though it was my insurance and offered to send photos of the accident (since I had already talked to them and they seemed to not understand it was not my fault).
Right away the fella said " you have photos?" and I said of course. He said it would not be necessary and hung up.
Later I realized it was the other sides insurance, and they paid for all the repairs without issue.