The Apple File System (AFPS), released with the macOS release 10.12, was designed and developed to take advantage of smaller solid state drives that are typically used for the operating system of the Mac hardware.
The key advantage of APFS is its ability to “copy to write” a snapshotting feature that enables better performance when copying large amounts of data. This, however, leverages the way solid state drives operate, and is not applicable to the spinning HDDs used in the SymplySPARK. So on the macOS it is best to leave the SymplySPARK formatted as macOS Extended (Journaled) file system as it ships from the factory.
If you have any questions please submit a [support ticket]