Neither can I but I plan defensively to accommodate blanket laws that may be invoked for some random control or minor traffic infringement. Not to mention some difficult traffic cop who has had a bad day and just itching to throw the book at someone.
My satnav is not at windscreen height and so intruding on any vision ahead. Instead it is embedded in the consul where the radio usually is on most cars. In fact, that is more dangerous in my opinion as it needs taking the eyes off the road to see it. It is rarely ever used and when it is I rely on the voice commands.
I believe that any 'video' appliance is illegal in the UK if the driver can see/watch it whilst the vehicle is in motion. An exception is made for equipment that is destined to aid the driver (e.g. navigation aids).