For those of you who have a rapsberry pi laying around (or need an excuse to buy one), you can set this up yourself.
I've installed it on a Raspberry Pi Zero 2 W and it works as expected. Only downside I see is switching between my and my wife's device (the Motorola device has a physical button for this).










One is enough for my setup. It depends on the car though, the raspberry needs 2 A /10 W. If your car doesn't provide enough energy, you might need another power source (e.g. a small power supply powered by that cigarette port.)