I have a next base dashcam, which gives decent pictures - if you get it from Halfords, they'll hard wire it for about £35. The advantage of this is that it's then "live" all the time and may get the reg of someone who drives into your car when it's parked.
Some police forces will accept dashcam footage to report alleged offences - check your local one's website. The potential problem with them is that they can be a bit of a double edged sword and used to provide evidence against you.
From a punting point of view, there's no need to worry about footage giving away where you've been, as they record a 5 minute loop, which is constantly overwritten unless it senses a crash, or you tell it not to. Afaik, they have no active tracking capability, so you can't be remotely checked up on, unlike your phone, which can.
A positive thing is that some Insurance Company's give a bit of discount if you have one.