If you want to setup the gnubee be sure to have a good enough power supply and use https://github.com/neilbrown/gnubee-tools instead of the official firmware. I would cross compile it since the compilation on the gnubee didn't provide me with a working image, but Neil browns effort getting a nearly mainline kernel to work are fabulous.

There are a few pitfalls so make sure to check your devices Mac address before and after the install. Also do a rudimentary performance check on the HDDs with hdparm. I was disappointed at the gnubee as well because of the (IMHO) stupid design decisions with the bootloader and the bugs it entails when running a newer system from an SD card. (You have to name your partition a certain way and it changes to that partition halfway through the boot. Also they never really tried (afaict) to mainline uboot and the version they used is ... not nice.

I really wanted to like and to use it, but for me it was a bit unstable with a full bay and since I didn't want to buy a bunch of new 2.5" discs for a unstable system and my 2.5" discs I tested with were all just 250gbit doesn't really work for me