Ford's concern is the vehicle's data and control buss shows up in the OBD2 port ... it's what the OBD2 readers use to display the error codes. A couple of years ago a pair of hackers demonstrated how a control buss hack could give them complete control of the vehicle, first from a wifi computer in the back seat, then via the cellular connection to the entertainment system from anywhere in the country. They were able to completely control the car, including things like steering, brakes, and the engine and transmission.
Then they demonstrated what they could do by taking over control of a Jeep Cherokee while a reporter was driving it:
https://www.wired.com/2015/07/hackers-remotely-kill-jeep-highway/
Needless to say, this scared the crap out of the auto industry and Chrysler quickly issued a patch to close the hole the hackers used.
A wireless device that plugs into the OBD port would give the same kind of vulnerability if it connects to the vehicle's data buss.
However, the Mobley does NOT have the ability to connect to the data buss - there are no physical connection to those pins - so there's no way anyone can use it to hack into the car. All it does is take a small amount of DC power from the OBD2 socket. The only problem you'll have is if the car turns off the 12 volts going to the port when you turn off the ignition.
What I wonder about are the new generation of OBD2 readers that use a PC or Smartphone to display the OBD codes.
It sounds like this can give the same kind of access that was used in the Chrysler/Jeep hack via the entertainment system. All anyone would have to do is modify the program running on the PC or Smartphone.