To be blunt, but I hope not unkind, what you think is not relevant. Aviation legislation prohibits the use of any electronic/electrical equipment on aircraft for which that aircraft is not approved. The approval may be a general one, as in mobile phones, or may be more specific.
A Garmin GPS has been approved for use in aircraft...it has been tested by the FAA...and it says so in the instructions. OK
what I think isn't really relevant but if a GPS can mess with stuff in an airliner it can mess with stuff in my all-singing, all dancing airways certified spamcan (not that I own one) which is worrying.