In WordPress, Jetpack has an ‘Image Compare’ feature. You add two images in it and it adds a slider in between. You can move the slider to see more portions of one image. An example can be found here: https://avif.io/
So recently, we moved from WordPress. I was under the impression that the image compare won’t work in Ghost as it was a feature provided by Jetpack plugin.
But to my surprise, it works the same in Ghost as well.
It’s an unfinished alpha feature that isn’t supposed to be used outside of core development - the alpha toggle list is there to enable the core team to selectively enable pieces of code whilst working on them without having to manage the nightmare of long-running git branches.
None of those features are ready to be used in live sites and you will run into usability issues or problems upgrading at some point if you’re making use of them.
If code is finished it will be released in a normal release or if it’s ready but needs wider testing then the feature will be promoted to beta and be available to everyone on the labs page.