I've used anti-glare screen protection on some of my devices. It's better than nothing, but it's still not great. Screen brightness all the way up and angle it away from the sun when possible. Map reading might be tricky in direct sunlight, but I seem to do okay with a black-and-white cue sheet. Of course full brightness drains the battery faster, so I've never tried to use my device like a dashboard GPS, just as a reference source to determine where and what the next turn is.