Not sure that the car satnav transmits out..... I thought they only received info from a paired device.
I can't see why a car satnav would have the facility to transmit spoken instructions as they have a speaker. I have checked my TomTom car satnav and can't get a thing out of it.
I have also have a Tom tom rider 2 and a Garmin zumo 660.
The mount for the Tom tom is so poor and failed 4 times so it is now sat in a drawer in disgrace! The zumo is superb in terms of quality, but the mapping is pants compared to the Tom tom...
I would choose the zumo, and ignore it's more bizzare mapping choices!