I thought I’d resurrect this old thread with some information on the iPad Pro. With iOS13 and an iPad pro, you can use a USB-C to USB-mini cable (like this $4.75 little one https://www.monoprice.com/product?p_id=14832). No dongle required.
When you plug the OP-1 in and turn on disk mode it will appear in the Files app, and you can copy files around. You can even “play” the tape tracks while they are still on the OP-1. Super handy for moving samples from the OP-1 to iOS based music apps.