Dont they all have both ?
As to visual motion detect i haven't heard of any one that dont work, the problem more often seem to be it work too good so you get a lot of events created by every little movement in front of your car.
The problem seem to be you cant set sensitivity to just react to something the size of a human or a car, and depending on how and where you park you will still see a lot of big things pass by and create a recording, and if too sensitive then you also get birds passing by - cats or leaves - branches or some one walking by on the other side of the large parkinglot and then you might as wall record all the time in some cases.
The G-sensor are what i would rely on for parking guard, but this i have not experimented on myself to actually see how much or little it would take to set it off.
Ideally you would want it sensitive enough that it get triggered if the car beside you slam his door into the side of your car, but at that setting i assume a passing bus or large truck might also set off a event.
But that still happen a less often than something moving in front of your car in a parking situation.
I did experiment with visual parking guard and low light with my lukas back in the day and it actually worked better than i expected, but i never got around to do the same with the G sensor, but using that for a short time while driving i did find that it was hard to set up and not having it create a event every time i brake or run over a tiny bump.
But i should have tried to see how little a push or kick of the tire would set off G sensor while in parking mode.
So my ideal parking setup would use G sensor, and maybe in the future a audio sensor ( glass break sensor )
Just try and see if you can see what set off this motion parking event.