I use HyperBackup to mirror my Synology NAS to an external hard drive. However, as a mostly-Mac user, I prefer that the external drive be readable by macOS too. (Sadly, ext4 support on a Mac requires third-party software or hacks.)
This is only a minor problem, as the latest Synology DSM does support read/write to HFS Plus drives. However, HFS Plus Journaled disks are not supported.
If you try to use a journaled disk with a Synology, you don't receive an error message. It simply won't mount the drive. (And, in my experience, might require you to reboot the entire NAS to recover.)
As of macOS High Sierra, Disk Utility no longer allows you to turn off journaling. You can do so using the comment line, though. Here's the incantation:
$ sudo diskutil disablejournal /Volumes/[diskname]
Interestingly, DSM will create a tiny ext4 partition on the HFS disk when mounting the drive. This partition remains invisible on macOS and can simply be ignored, except for making sure you choose the larger, HFS partition for the HyperDrive destination.