i have motionx gps drive and it SUCKS!
do not buy this apps extra features, its not worth it. i paid extra for the external display feature, and it does nothing that a mirror app cant do. you cannot control the gps from the screen or any features for that matter. if you want to listen to music, it has to be controlled from the iphone itself. the screen basically is there just to display and thats about it. the app uses its own media player to play music. in order for you to use it, you have to manually select all the tracks you want to listen to. even if you already have playlists setup, you have to select either the tracks individually or select all songs and then hit done. the quality is horrible, it sounds flat, and as if your listening to the music through head phones. if you want to change the track, you have to do it through the iphone.
as a gps on its own its great, but when used with the 8400 its waste of money and i want a refund.
i also tried the other gps app, navfree. i have no idea if it works, because it would not let me listen to any music when i was using it, so i quit it almost immediately
im shocked and saddened that none of the 2 gps apps are worth anything. had i known, i seriously would have considered waiting for the new clarion. i cant believe pioneer dropped the ball this bad