According to the below linked article:
"Storage Expansion Cards are fast enough to install your operating system onto and you can boot from them too."
Anybody found this to be an issue? Thanks!
I dual boot with Grub2 for Ubuntu on the expansion card, it takes 7 seconds to bring up grub, then another for Ubuntu or Win 11.
I have Win 11 on the NVMe, the only issue of course is that if the Expansion card fails I can’t boot.
But I usually use Windows so once there, that wouldn’t happen, plus I usually use hibernate so Grub2 doesn’t get called that often.
Expansion cards can disconnect now and then, and auto reconnect so can be an issue.
It is not recommended, it’s not the speed but the unreliability with some setups. You may have problems in the lower two expansion slots for example
YIKES
is that a thing…!
Good idea to search before you start a topic 
https://community.frame.work/search?q=Expansion%20card%20disconnect