Hey Paul,
this is still often claimed, but it is not true. USB 3.0 flash drives work perfectly on the Onefinity Controller, because every USB 3.0 device is downwards compatible by design.
What might not be supported because of the age of the underlying Operating System in the Onefinity Controller, is exFAT Filesystem found on practically every USB drive bigger than 32 GB nowadays. If your flash drive is not recognized by Onefinity Controller, you have to reformat the flash drive using NTFS or FAT32 instead. 
exFAT Filesystem is supported natively since Linux kernel 5.4 but I have no idea if or when Onefinity will switch to a newer version of the underlying OS.