The ONE App is primarily intended for use with an internet connection because the audio tracks are streamed directly to your computer or phone.
We are currently creating native apps for iOS and Android devices that will be available later this year.
Each track and also be downloaded individually within the ONE App player web page. The process works well using a desktop computer, but can be tricky on a phone. Every phone handles the process a little differently based on the user's settings, and we find that most people have a difficult time with files being out of order and/or having trouble finding the files.
The following video explains downloading in more detail.