It is mostly due to Unraid's infancy with ZFS (if I was guessing), it wouldn't automatically start the array if you had them added as an L2ARC. That was on the pre-release version, it may be fixed now, I just gave up on trying to resolve it in all honesty. The drives themselves work well.
Supermicro was very quick to tell me to pound sand when I requested this be added to the bios. Makes sense because I'm just an end user, but I won't be purchasing from them again. I also am friends with the IT support for a couple of the hospitals that I work in and will suggest they do the same.
Yeah it is disappointing. I really came to SM because I thought they had good support, but when Asus has better support/features something is wrong. I'd love to pick up an Intel Arc card for plex transcoding when it's supported, but no re-bar support really holds them back.