I've spent the past week looking at dash cams, the Nextbase 512g gets about the best reviews for the money and has a decent lens with a polarising filter, I nearly went for it but felt its slightly too large/baulky so have gone for a Transcend DrivePro 220 from Amazon for 130 quid and ordered an additional mounting bracket and power adapter for the other car. I don't think its the best but I find the difficulty is getting a decent size smallish cam combined with good quality recording.
https://www.youtube.com/watch?v=QCyd9RFi8yY
I've bought a fair few cheaper end of the market dash cams when I mean cheaper less than 100 quid and would say they are a complete waste of money as I've found they tend to underexpose and unable to cope with bright light conditions and the lens quality tends to be poor so are not capable of capturing reg plates which is what you need in the event of an accident.
Cam has arrived today so will fit it tomorrow and see how it fares.
Tim.