My CrystalSky Ultra now has more storage space than my desktop pc 
I bought this one in the end:
https://www.amazon.co.uk/gp/product/B0196J3UZ2/
First thing I did when it arrived was format it to NTFS ( @SteveM ) 
It came with a load of pre-loaded Seagate backup utilities too, no use to me though.
The CS powers the external drive with no issues. Reports its size correctly too. I put the MicroSD card from the Mavic in to one slot on the CS and copied all manner of files (large and small) directly to the hard drive. Sorted 
Thanks everyone 