I have blackvue (just front) on mine
Front and back on one car
And front and back on the work van
The picture qaulity is excellent, they're quite stealthy and have some very good features with the way they save videos, you can change the sensitivity on the movement sensors, WiFi connection, GPS (you can turn on/off), speed readout (you can turn on/off) and loads more. Only thing is the voice recording is pretty poor as the road noise is nearly all you can here but it doesn't matter much and you can turn it on/off.