We had front and rear dash cams fitted by Halfords, just before Christmas, as we had just had a new car.
I think they are the same as in the link posted by SueDonim
Thankfully we haven't had to use the recorded info, yet.
You really don't need a big screen, and there may be a limit anyway, as you don't want it to get in the way of your vision.
Just as we were driving into the fitting bay at Halfords, a lady came speeding out from a side road, and didn't see us. Luckily we were going cautiously, looking for the turning.
If she had hit us, it would have been evidence against her.