So, yeah, been using CORE for forever. Back to the V8 days. I have dabbled with SCALE a little but my first real try was with 25.04.01 - disaster as Virtualization was borked as we all know.
So, I was excited to see 25.04.02. Not excited any more.
Issues I had:
ALUA iSCSI issues with ESXi - this was a bear to solve - like a real dog (well, made worse that on ESXi system worked and one did not…). The CORE iSCSI system seems way more solid wrt iSCSI.
Permissions - what sociopath back in the day though it would be a good idea to use GID 20 for Staff in BSD and GID 50 for Staff in Debian… Just lame. Even better is that GID 20 in Debian is “dialout”… This was going to be a major PITA to unravel.
Accounts - So, why is it not possible to add users to auxiliary groups suddenly? That sucks a lot. Also, and this is my bad from OS X, but capital letters in users apparently is bad in Debian. Legacy fun for me.
Virtualization - yeah, hmm. It “works” kinda. Managed to fail at hitting the gosh darn spacebar to boot from the ISO. This was after I finally massaged the system to access the ISO directory (one would think the builtin-administrator account could access anything it wanted to…). Not chuffed I would say. But at least Virtual TPM was back!!
Stability - I run iSCSI over Twinax through one would call a “cheap” hub. Yes it is not fancy but it works flawlessly in CORE with ESXi. On SCALE, 1 of the 2 links would go to ZERO receive traffic after a few minutes. Tried different ports, tried swapping cables, problem stayed with one interface (card is a 2 port card). This was fun…
Scripts - yeah, this will always be a PITA when migrating but man alive, converting shell scripts is a hassle. Got a couple sorted (the ones I wrote) but others that I have scored from the forums (fan PID control, SMART reports, ESXi commands) are a bit more work. I figure my time is worth more than the power it costs me to run 2 hosts instead of 1. 
The only reason that I am interested in SCALE is to get away from running ESXi at all (Broadcom is evil). I used to run TrueNAS on top of ESXi for years and it was good. Tried to do the same with Proxmox, but it was flakey. Reverted back to separates as it is stable. Was hoping I could use SCALE as my 1 box solution but I think the juice is not worth the squeeze and that TrueNAS SCALE is just not ready for this yet.
Sucks that CORE is mostly EOL - but it just works. Solid, stable, functional NAS. At least reverting was simple as swapping boot disks (and thank the tech nerds I did not update the ZFS feature flags…).
Hopefully some day SCALE can be an option for me, but currently it is not. Keep up the good work TrueNAS team and I will continue to follow the progress.
Cheers,