The mod does what it says, but what if I want to see the slots preview by default?

There doesn't seem to be an option for that currently, only for swapping between "tooltip types" (aka preview text) and "modes" (shift vs alt+shift).

Using v1.1.2 on Fabric (1.14 release)

Good idea, I have not thought about that!

I added an 'alwaysOn' config option in the 1.2.0 version of the mod