Hi Thomas,
I’m a new +plus member and maybe someone here has a better way of doing it but I’ve been able to download the ‘member’ content and listen to it ‘offline’ (no data charges) 2 different ways, both of which requires you use your PC or Mac.
1) Using your PC ‘Right Click’ and download the .mp4 files and import them into iTunes library and then sync your iPhone or iPad.
2) Using your PC ‘Right Click’ and download the .mp4 files and then right click on the .mp4 file you downloaded and save it to DropBox on your PC. Then from your iPhone or iPad you can go in and designate which files you want ‘offline’ view-able. DropBox comes with a simple audio player that plays .mp4 files. The DropBox Basic account comes with 2 GB of free space and I’ve never had the need to to upgrade it to the ‘paid’ PRO version…
Hope this helps! 
Garry