I recently used the F6-424 (which barring the number of bays should be the same I think), it was pretty easy overall. I updated the ram and added an NVMe M.2 drive to install HexOS onto. Here are some things to note or consider:
-There is an issue with with some of the BIOS settings for the Terramaster and how it interacts with TrueNAS/HexOS, and after changing some settings I was able to solve those issues and it seems stable. (though its only been a couple days, but the rolling restarts no longer happen)
Here is a link concerning the settings in the BIOS that should be changed from someone smarter than I:
-As many guides/ videos point out, you will need a low profile USB imaged with HexOS to replace an existing USB that can be accessed by taking the right side of the case off, and removing the board under it, where the memory and M.2 slots are, it is located on the underside of that board.
-It was recommended that after HexOS is installed to shut down the system and remove that USB because there is a tendency for the system to occasionally attempt to boot from it after install which can increase start up times for your server. I saw a video claiming that you could use the exterior USB and alternatively get to the BIOS to change the boot order, but most people said that it didn't work that way for whatever reason and you would want to remove the USB anyways.
-During this process it was recommended to update the RAM as TrueNAS, and I imagine HexOS by proxy, will take advantage of it.
This is my first NAS, and though I haven't done anything beyond using it as storage/ backup thus far, I found the hardware easy to work with and if you know to change the BIOS stuff indicated in the linked post then it seems to run fine. I will say this is not the most cost efficient way to have a NAS and it comes with the drawback of giving up some ability to upgrade in the future, but if your looking for a compact solution this works well and though I can't say that Terramasters software is great, I have seen people recommend their hardware.
I hope this helps.