Linux & tomtom
The tom tom linux implimentation seems simple: you can see the file system in usb connection, and the whole experience is straightforward and unremarkably simple. It plays music from an mp3 directory and displays graphics from a picture directory. What's not to like?
Unfortunately the 'home' application needed to manage maps runs only on windoze, and there seems no excuse for that. When you are running it, however, it does everything you want. Although moving maps from the internal memory to the SD card requires an act of faith. You have an option to copy maps to the PC and to delete them. The obvious 3rd step, to copy them back to the device, is there but not visible until the situation arises. So the 'home' application ergonomics could be better, but it actually does everything it needs to.
But the overall package is excellent, and I think they remain the market leader, although I am not happy about their lastest pricing either for hardware or for the more advanced subscription services. I think they have started milking the cow.