I have flown with friends with really good moving map GPS. They are great tools.
My concern is that they -and they may well be in a minority - have developed a habit of sticking firmly to the pre-determined route. Not sure why!
I'm all in favour of this type of GPS to help in diversions, within limits. What does worry me are pilots, such as the one I encountered on Saturday, ploughing a furrow between two waypoints and failing to make a turn to avoid a head-on collision.