I use every day the native music player and the ebook reader function. Both of them suck for some reasons (audio player: crashes, bad audio effects, both effects and equalizers cause output saturation, no playlist support... ebook: no support for italian accents, background color has to be setted every time you boot your dingoo, ugly font, no page rotation, ...), but I like the fact that I can start listening to songs when i get in train and start reading later, without stop playing, that makes them the more comfotable solution.
I hope they both could be soon replaced by greader2x.