For Car Thing to really be useful for me, it needs act as a Bluetooth receiver with it's own AUX output port so it can always be connected to my car.
My car has an AUX input that I plug into my phone and then mount my phone horizontally on the window. This creates almost the same thing as Car Thing. The annoying step with the whole process is remembering to pull my phone out of my pocket and plug in the AUX input every time I get in my car. On shorter drives I don't bother with the whole step of plugging my phone in and mounting it. What I need is for Car Thing to become my Bluetooth receiver that is always plugged in and ready to go when I start my car. Otherwise it's just adding another cord dangling from my dashboard, and a redundancy to my current setup.
I feel like the point of Car Thing is to reduce distracted drivers, but if someone doesn't remember to plug their phone in before driving, it's not solving the distracted driver fumbling for their phone and searching around for the AUX cable while on the move. In my other vehicles with Bluetooth, I can just get in and it starts playing. That's what this needs to be.
If thickness is a concern for adding this component, maybe there could be 2 options, 1 that's a Bluetooth receiver with AUX output, and 1 that's not.