I am using a 2nd gen 12.9” iPad Pro with 512gb storage.
When in the field / whilst travelling I transfer video from my CFast 2.0 reader (for Canon 1DX2 - so very large file sizes with high bitrates) to either the WD My Wireless Passport Pro 4TB (and then transfer wirelessly to the iPad Pro) or more recently the LaCie DJI CoPilot BOSS 2TB (and transfer direct to the iPad Pro via the attached Lightning cable). On the go I edit photos on the iPad in Adobe Lightroom and video in LumaFusion 2.0.
I picked up the WD My Wireless Passport Pro 4TB as a backup and file transfer solution before going to Europe filming for a month last year, and I was only taking my iPad rather than a MacBook. I had wanted the Lacie DJI, as a wired solution, but at that time it was still not released in Australia. I also looked at GnarBox, but in hindsight it is just as well that I did not wait for GnarBox 2.0. Whilst I was able to backup my data on the go, and make a further backup to a Lacie Rugged Drive from the WD Wireless Drive when staying with friends and using their Mac or PC, it is a slow solution to transfer large video files from the WD to the iPad.
My subsequent experience with the Lacie DJI CoPilot BOSS drive has been more flexible and reliable, and this is now my preferred backup whilst away from home. For several months I used it as my main data transfer device to the iPad via the lightning cable, and you can transfer multiple files at once if they are in a folder to store in iOS Files, or alternatively 'share' them a file at a time with LumaFusion (which is a tad laborious). Both the WD and the Lacie create a duplicate in iOS Files, and the only way to clear data that I have found is to uninstall each app once in a while... but this is an iOS 12 failing rather than a WD, Lacie or LumaFusion issue.
When in the studio with both my Mac and iPad, the most efficient and super fast transfer method between Mac and iPad (and vice versa) is with AirDrop - and as long as multiple videos are in a single folder, AirDrop will shift the folder into Files on the iPad. I have sent folders of up to 40gb so far, and When prompted I just locate them in the ‘User Media’ folder in ‘LumaFusion’ in iOS Files. As a result, I am not sure what the hype with iPadiOS is, as all the functionality for file management already exists in iOS 12.
The challenge for me is managing data on the iPad, as LF seems to have a duplicate of data in the iOS Files app, so a 512gb device is only good for around 200gb of data.
Hope this helps,