As I understand it, enabling certain ZFS flags in Cobia can make the drives incompatible with Bluefin. How is that "portable"?Nonsense, it's the most portable filesystem capable of storing files larger than 2 GB (technically FAT32 is more widespread, but that's only still relevant because of UEFI).
NTFS can be read by every modern OS out there along with some that aren't so modern (ie. MS-DOS).
Such is not to say that NTFS is ideal in any other way but it is hard to beat for interoperability.