I moved my OS over to FreeNAS (while using the same hardware) to test if the slowness currently experienced on macOS (v 1.7.n) was not intrinsic to the drives, nor their setup/initialisation.
This was using 8 mirrored 4TB SATA Seagate Barracudas ST4000DM004 which flew! So no issue with moving between platforms. (assuming you don't push zpool updates)
I've since moved back to macOS because I have absorbed the slowness to a degree with installing 10GB switches and wish to show support to the macOS devs as much as possible too.
Having said that, I've also installed
NAS4Free onto a spare rig and am testing
SyncThing to backup onto 3 x 12TB IronWolfs in RAIDz for another backup at the folks house.
I noticed a few issues with FreeNAS's addons/services that didn't want to install for me, which is why I stuck with the original developer who's now developing NAS4Free.
I did notice that FreeNAS created a new dataset on my existing pool called $poolname/.system, so I simply deleted that once my testing was done.
Whatever you do, insure that the pool you create under any non macOS platform has the attributes of normalization=formD & casesensitivity=insensitive, so that you look after macOS's semantics, or just move your disks over like I did. (NAS4Free has a "syncronise command that syncs the disks to the web GUI for you… neat!)
Cheers,