I bought 4k forward and rear for my car. I had to contact support three times: to query whether it could be used without the smart phone app (it can), to confirm my exact model after ordering and because I couldn't find where to plug it in on my car because it was different from the video. Each time the turnaround was fast and immediately remedied the situation concisely.
The camera itself simply records your journey in x265 ts files rotating the files every 2 minute. There are separate files for front and rear cameras. It comes with a 128G micro SD card and you create about 7G for the 4k front camera and about 4.5G for the rear camera per hour so that's about 11 hours travel time before it needs to start deleting files.
You can join the 2 minute files together with ffmpeg
ffmpeg -f concat -i list.txt -c copy all.mp4
where list.txt contains a file list for the files you want to join which you can create with something like this is bash
for i in $(ls *.TS); do echo "file $i"; done > list.txt.
Anything that will join transmission streams together will work. The cameras create standard x265 files.
The cameras themselves are up to the task. You will need to be close to read a number plate - maybe 10-15m but they deal with changing light conditions reasonably well and provide a good usable quality. If you don't expect pristine 4k video from something that would cost 5x as much and take up much more space, I don't think you'll be disappointed.
The polarizing filter for the front camera is extremely large and will draw a lot more attention to the camera. I decided not to fit it for that reason. The cameras themselves are relatively innocuous. You can see them if you're looking for them but they won't draw much attention. The color of the housing for my camera did not match the color of my car interior: it was grey my car is beige. Again, this is something you notice when you're looking for it but otherwise isn't too problematic.
Overall, I'm extremely happy with these cameras. They do exactly what I want without a cumbersome screen, don't draw attention to the car and have so far been very reliable. Great engineering. I haven't used the smart phone app, so I can't comment on that.
I would write the same review on trustpilot.