The player is undeniably awash with features. On the audio side, it will play MP3, WMA, ASF and the ultra-efficient Ogg. Only the Apple-flavoured AAC is conspicuous by its absence, though that's hardly surprising. It can also record to MP3, either from the built-in microphone or from the built-in FM radio. It can also play back video, though only at 15fps.
However, for all its good features, design and navigation, iRiver falls down for the same reason that every other PC-focused manufacturer does - getting content onto the device itself. The U10 uses no less than three different methods.
Firstly, music can be transferred using Windows Media Player. To be fair, this works quite well. WMP might not be as good as iTunes, but once you get to know its quirks you'll be transferring your tracks in no time. However, if you want to transfer pictures you have to use the supplied Picture Plus application. This is because pictures need to be converted to a proprietary format rather than just copied over. The software does enable you to place pictures in their own folders and when you copy your pictures over the metadata contained in the file is displayed too.
Videos, on the other hand, are copied over using Windows Explorer. For some inexplicable reason the video folder isn't a sub-folder of the Media folder, but is in the Data folder. The iRiver can only play back video in a very specific AVI format and rather short-sightedly, no utility is supplied to convert video. Fortunately, there are third-party conversion tools available, and with judicious compression you can fit a couple of full-length movies on the 1GB player and still have room left for music and pictures. However the screen is so small, watching shorter things like TV episodes might be more suitable.