Thanks for the clarification - you are correct on both counts, with the exception of small functionality like the console preview. Doing the upgrade was still worth it to me since it got rid of all the annoying in-browser prompts to upgrade/install Java, and made the console preview work again.
I'm not usually a FreeNAS release early adopter, but I decided to make an exception today because of the nasty Samba security vulnerability. I just upgraded from 9.10.2-U1 to 9.10.2-U4 (hot off the presses!) and had no issues. Also, it really does give you Samba 4.5.10, despite the fact the the change log says 4.5.9.
Thank you for this. The funny bit is, I went down the path of using this same hardware BEFORE seeing your thread, but your thread really cleared up a bunch of stuff for me. My beast doesn't have as much space on it, I only have 24tb addressable because raidz2 -- but she's truly a beast.