‘Move to USB’ isn’t about speed, you don’t need fast cards for OH to work.
It’s meant to protect the user from SD corruption of the boot disk, but it’s just a half-hearted approach since #1 it still uses the internal SD card (although for a lot less writes) but (even more important) #2 most people use a USB stick, and that one corrupts as easy as does the internal card, so in the end it doesn’t really buy you anything unless you attach something more reliable than flash memory to USB.
If you’re looking for resiliency, check out this post.