Total screen blackout while driving is a bit too much lockout. Data entry or any user interaction lockout is understandable, but screen with map and car's position, direction of motion etc., should continue to display. Quick glance on where your car is, upcoming road curve and turn direction etc., are very useful. My ES350 is non-nav, I use Garmin nuvi and glance on the map every now and then, when at stop light, etc.